Mental Model Encyclopedia (Master List)
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Jeff Bezos
Dave McClure
Andy Rachleff
Balaji S. Srinivasan
Paul Graham
Frank Robinson
Ray Dalio
 Robert Metcalfe
Adam Smith
Clayton Christenson
James ClearShane ParrishGabriel WeinbergScott Page
Charlie Munger
Daniel Dennett
Jack BarkerHiten ShahBrandon Chu
Founder of Amazon
Founder of Y Combinator
Harvard B-School Professor
Serial Entrepreneur & Author
Founder Of Farnam Street
Serial Entrepreneur & Author
GM, Platform @shopify
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General Thinking ToolsInversion"Otherwise known as thinking through a situation in reverse or thinking “backwards,” inversion is a problem-solving technique. Often by considering what we want to avoid rather than what we want to get, we come up with better solutions. Inversion works not just in mathematics but in nearly every area of life. As the saying goes, “Just tell me where I’m going to die so I can never go there.” - Shane Parrish

"By imagining the worst case scenario ahead of time, they could overcome their fears of negative experiences and make better plans to prevent them. While most people were focused on how they could achieve success, the Stoics also considered how they would manage failure. This way of thinking, in which you consider the opposite of what you want, is known as inversion.Inversion is a powerful thinking tool because it puts a spotlight on errors and roadblocks that are not obvious at first glance. " - James Clear

"Many problems resist being solved “from the front.” They demand that you solve them backwards or from an unintuitive angle. This is the art of inversion. Sometimes the question should not be: “What features do we build?” Rather, it should be: “What features would destroy this product?” Once you know which features are going to run your product into the ground, you can achieve a simple win just by not doing those. For PMs, the label of “CEO of the product” can sometimes tempt them into over-relying on their instincts when it comes to building product. However, it is much easier to avoid making mistakes than it is to be perfect all the time. Inversion is also a powerful way to break out of the repetitive thought-loops that can hurt your team’s ability to learn. We can easily fall into “retro-fatigue” asking questions like, “How can we innovate more?” or “Why did that project not go well?” over and over again. Our brains go on autopilot and start giving similar-sounding answers. That is why asking questions like “What can we do to innovate less?” can be such a powerful rhetorical technique. It provides you with a slightly different point of view—but one that is usually much more insightful." - Hiten Shah


Instead of starting at a problem and then exploring towards a solution, start at a perfect solution and work backwards to today in order to figure out where to start.

How it’s useful

Most teams tend to work forwards, which optimizes for what is practical at the cost of what’s ultimately impactful.

Working backwards helps you ensure that you focus on the most impactful, long term work for the customer because you’re always reverse-engineering from a perfect solution for them.

Note that working backwards isn’t universally better, it just creates a different perspective. It’s healthy to plan using both perspectives.

—Brandon Chu

Shane Parrish's Farnam Street Mental Model Guide

James Clear Mental Models Overview


Hiten Shah's 3 Mental Models Every PM Needs to Make Decisions


Product Management Mental Models for Everyone -
Arguing from First Principles“A first principle is a basic, foundational, self-evident proposition or assumption that cannot be deduced from any other proposition or assumption.” (related: dimensionality reduction; orthogonality; “Reasonable minds can disagree” if underlying premises differ.)Gabriel Weinberg's Mental Models I Find Repeatedly Useful0
Falsification / Confirmation Bias"What a man wishes, he also believes. Similarly, what we believe is what we choose to see. This is commonly referred to as the confirmation bias. It is a deeply ingrained mental habit, both energy-conserving and comfortable, to look for confirmations of long-held wisdom rather than violations. Yet the scientific process – including hypothesis generation, blind testing when needed, and objective statistical rigor – is designed to root out precisely the opposite, which is why it works so well when followed.

The modern scientific enterprise operates under the principle of falsification: A method is termed scientific if it can be stated in such a way that a certain defined result would cause it to be proved false. Pseudo-knowledge and pseudo-science operate and propagate by being unfalsifiable – as with astrology, we are unable to prove them either correct or incorrect because the conditions under which they would be shown false are never stated."- Shane Parrish

“The tendency to search for, interpret, favor, and recall information in a way that confirms one’s preexisting beliefs or hypotheses, while giving disproportionately less consideration to alternative possibilities.” (related: cognitive dissonance)" - Gabriel Weinberg

“It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than by negatives.” — Francis Bacon
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful

Thucydides via 13 Mental Models Every Founder Should Know
Circle of CompetenceAn idea introduced by Warren Buffett and Charles Munger in relation to investing: each individual tends to have an area or areas in which they really, truly know their stuff, their area of special competence. Areas not inside that circle are problematic because not only are we ignorant about them, but we may also be ignorant of our own ignorance. Thus, when we're making decisions, it becomes important to define and attend to our special circle, so as to act accordingly.Shane Parrish's Farnam Street Mental Model Guide11
The Principle of Parsimony (Occam’s Razor)Named after the friar William of Ockham, Occam’s Razor is a heuristic by which we select among competing explanations. Ockham stated that we should prefer the simplest explanation with the least moving parts: it is easier to falsify (see: Falsification), easier to understand, and more likely, on average, to be correct. This principle is not an iron law but a tendency and a mindset: If all else is equal, it’s more likely that the simple solution suffices. Of course, we also keep in mind Einstein’s famous idea (even if apocryphal) that “an idea should be made as simple as possible, but no simpler.” - Shane Parrish

“Among competing hypotheses, the one with the fewest assumptions should be selected.” (related: conjunction fallacy, overfitting, “when you hear hoofbeats, think of horses not zebras.”) - Gabriel Weinberg

"Don’t concoct a complicated, extravagant theory if you’ve got a simpler one (containing fewer ingredients, fewer entities) that handles the phenomenon just as well. If exposure to extremely cold air can account for all the symptoms of frostbite, don’t postulate unobserved “snow germs” or “arctic microbes.” Kepler’s laws explain the orbits of the planets; we have no need to hypothesize pilots guiding the planets from control panels hidden under the surface." - Daniel Dennett
Shane Parrish's Farnam Street Mental Model Guide via


Gabriel Weinberg's Mental Models I Find Repeatedly Useful via

Philosopher Daniel Dennett's Book Intuition Pumps
Hanlon's Razor"Harder to trace in its origin, Hanlon’s Razor states that we should not attribute to malice that which is more easily explained by stupidity. In a complex world, this principle helps us avoid extreme paranoia and ideology, often very hard to escape from, by not generally assuming that bad results are the fault of a bad actor, although they can be. More likely, a mistake has been made." - Shane Parrish

“Never attribute to malice that which is adequately explained by carelessness.” (related: fundamental attribution error — “ the tendency for people to place an undue emphasis on internal characteristics of the agent (character or intention), rather than external factors, in explaining another person’s behavior in a given situation.”) - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide via


Gabriel Weinberg's Mental Models I Find Repeatedly Useful via
Second-Order ThinkingIn all human systems and most complex systems, the second layer of effects often dwarfs the first layer, yet often goes unconsidered. In other words, we must consider that effects have effects. Second-order thinking is best illustrated by the idea of standing on your tiptoes at a parade: Once one person does it, everyone will do it in order to see, thus negating the first tiptoer. Now, however, the whole parade audience suffers on their toes rather than standing firmly on their whole feet.Shane Parrish's Farnam Street Mental Model Guide11
The Map Is Not the TerritoryThe map of reality is not reality itself. If any map were to represent its actual territory with perfect fidelity, it would be the size of the territory itself. Thus, no need for a map! This model tells us that there will always be an imperfect relationship between reality and the models we use to represent and understand it. This imperfection is a necessity in order to simplify. It is all we can do to accept this and act accordingly.Shane Parrish's Farnam Street Mental Model Guide11
Thought ExperimentsA technique popularized by Einstein, the thought experiment is a way to logically carry out a test in one’s own head that would be very difficult or impossible to perform in real life. With the thought experiment as a tool, we can solve problems with intuition and logic that could not be demonstrated physically, as with Einstein imagining himself traveling on a beam of light in order to solve the problem of relativity. - Shane Parrish

“considers some hypothesis, theory, or principle for the purpose of thinking through its consequences.” (related: counterfactual thinking) - Gabriel Weinberg'
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
Mr. MarketMr. Market was introduced by the investor Benjamin Graham in his seminal book The Intelligent Investor to represent the vicissitudes of the financial markets. As Graham explains, the markets are a bit like a moody neighbor, sometimes waking up happy and sometimes waking up sad – your job as an investor is to take advantage of him in his bad moods and sell to him in his good moods. This attitude is contrasted to an efficient-market hypothesis in which Mr. Market always wakes up in the middle of the bed, never feeling overly strong in either direction.Shane Parrish's Farnam Street Mental Model Guide11
Probabilistic Thinking (See also: Numeracy/Bayesian Updating)The unknowable human world is dominated by probabilistic outcomes, as distinguished from deterministic ones. Although we cannot predict the future with great certainty, we are wise to ascribe odds to more and less probable events. We do this every day unconsciously as we cross the street and ascribe low, yet not negligible, odds of being hit by a car.Shane Parrish's Farnam Street Mental Model Guide11
Default StatusThe USCB ecologist/economist Garrett Hardin once said that “The scientific mind is not closed: it is merely well-guarded by a conscientious and seldom sleeping gatekeeper.” The way it does that is with the concept of the default status: The “resting position” of common sense, whereby the burden of proof falls on assertions to the contrary. Given the problem of opportunity costs and limited time and energy, a default status is nearly always necessary to avoid wasting time. Examples include the laws of thermodynamics, the law of natural selection, and the incentive-caused bias.Shane Parrish's Farnam Street Mental Model Guide11
Making MistakesPhilosopher Daniel Dennett's Book Intuition Pumps11
Reductio ad AbsurdumThe crowbar of rational inquiry, the great lever that enforces consistency, is reductio ad absurdum—literally, reduction (of the argument) to absurdity. You take the assertion or conjecture at issue and see if you can pry any contradictions (or just preposterous implications) out of it. If you can, that proposition has to be discarded or sent back to the shop for retooling. Philosopher Daniel Dennett's Book Intuition Pumps11
Rapoport’s RulesHow to compose a successful critical commentary:

1. You should attempt to re-express your target’s position so clearly, vividly, and fairly that your target says, “Thanks, I wish I’d thought of putting it that way.”
2. You should list any points of agreement (especially if they are not matters of general or widespread agreement).
3. You should mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.

One immediate effect of following these rules is that your targets will be a receptive audience for your criticism: you have already shown that you understand their positions as well as they do, and have demonstrated good judgment (you agree with them on some important matters and have even been persuaded by something they said).
Philosopher Daniel Dennett's Book Intuition Pumps11
Sturgeon’s Law"Sturgeon’s Law is usually put a little less decorously: Ninety percent of everything is crap. Ninety percent of experiments in molecular biology, 90 percent of poetry, 90 percent of philosophy books, 90 percent of peer-reviewed articles in mathematics—and so forth—is crap. Is that true? Well, maybe it’s an exaggeration, but let’s agree that there is a lot of mediocre work done in every field...."

"Now, in order not to waste your time and try our patience, make sure you concentrate on the best stuff you can find, the flagship examples extolled by the leaders of the field, the prizewinning entries, not the dregs."
Philosopher Daniel Dennett's Book Intuition Pumps11
Occam’s Broom"The process in which inconvenient facts are whisked under the rug by intellectually dishonest champions of one theory or another."Philosopher Daniel Dennett's Book Intuition Pumps11
Using Lay Audiences as Decoys"In many fields—not just philosophy—there are controversies that seem never-ending and partly artifactual: people are talking past one another and not making the necessary effort to communicate effectively. When experts talk to experts, whether they are in the same discipline or not, they always err on the side of under-explaining. The reason is not far to seek: to overexplain something to a fellow expert is a very serious insult—“Do I have to spell it out for you?”—and nobody wants to insult a fellow expert.

Solution for this problem: Have all experts present their views to a small audience of curious nonexperts (here at Tufts I have the advantage of bright undergraduates) while the other experts listen in from the sidelines. They don’t have to eavesdrop; this isn’t a devious suggestion. On the contrary, everybody can and should be fully informed that the point of the exercise is to make it comfortable for participants to speak in terms that everybody will understand. By addressing their remarks to the undergraduates (the decoy audience), speakers need not worry at all about insulting the experts because they are not addressing the experts. (I suppose they might worry about insulting the undergraduates, but that’s another matter.) When all goes well, expert A explains the issues of the controversy to the undergraduates while expert B listens. At some point B’s face may light up. “So that’s what you’ve been trying to say! Now I get it.”"
Philosopher Daniel Dennett's Book Intuition Pumps11
Jootsing"Jootsing stands for “jumping out of the system.” This is an important tactic not just in science and philosophy, but also in the arts. Creativity, that ardently sought but only rarely found virtue, often is a heretofore unimagined violation of the rules of the system from which it springs. It might be the system of classical harmony in music, the rules for meter and rhyme in sonnets (or limericks, even), or the “canons” of taste or good form in some genre of art. Or it might be the assumptions and principles of some theory or research program. Being creative is not just a matter of casting about for something novel—anybody can do that, since novelty can be found in any random juxtaposition of stuff—but of making the novelty jump out of some system, a system that has become somewhat established, for good reasons."Philosopher Daniel Dennett's Book Intuition Pumps11
Three Species of Goulding: Rathering, Piling On, and the Gould Two-StepRathering is a way of sliding you swiftly and gently past a false dichotomy. The general form of a rathering is “It is not the case that blahblahblah, as orthodoxy would have you believe; it is rather that suchandsuchandsuch—which is radically different.” Some ratherings are just fine; you really must choose between the two alternatives on offer; in these cases, you are not being offered a false, but rather a genuine, inescapable dichotomy. But some ratherings are little more than sleight of hand, due to the fact that the word “rather” implies—without argument—that there is an important incompatibility between the claims flanking it.Philosopher Daniel Dennett's Book Intuition Pumps11
The “Surely” Operator: A Mental Block"When you’re reading or skimming argumentative essays, especially by philosophers, here is a quick trick that may save you much time and effort, especially in this age of simple searching by computer: look for “surely” in the document, and check each occurrence. Not always, not even most of the time, but often the word “surely” is as good as a blinking light locating a weak point in the argument, a warning label about a likely boom crutch. Why? Because it marks the very edge of what the author is actually sure about and hopes readers will also be sure about. (If the author were really sure all the readers would agree, it wouldn’t be worth mentioning.) "Philosopher Daniel Dennett's Book Intuition Pumps11
Rhetorical QuestionsJust as you should keep a sharp eye out for “surely,” you should develop a sensitivity for rhetorical questions in any argument or polemic. Why? Because, like the use of “surely,” they represent an author’s eagerness to take a short cut. A rhetorical question has a question mark at the end, but it is not meant to be answered. Whenever you see a rhetorical question, try—silently, to yourself—to give it
an unobvious answer.
Philosopher Daniel Dennett's Book Intuition Pumps11
What Is a Deepity?A deepity is a proposition that seems both important and true—and profound—but that achieves this effect by being ambiguous. On one reading it is manifestly false, but it would be earth-shaking if it were true; on the other reading it is true but trivial. The unwary listener picks up the glimmer of truth from the second reading, and the devastating importance from the first reading, and thinks, Wow! That’s a deepity.
Example: Love is just a word.
“love” is an English word, but just a word, not a sentence, for example.
Philosopher Daniel Dennett's Book Intuition Pumps11
Scientific Method“Systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses.” (related: reproducibility) - Gabriel Weinberg

"The scientific method is a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry is commonly based on empirical or measurable evidence subject to specific principles of reasoning.The Oxford Dictionaries Online defines the scientific method as "a method or procedure that has characterized natural science since the 17th century, consisting in systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses". Experiments need to be designed to test hypotheses. Experiments are an important tool of the scientific method." - Wikipedia (James Clear)
Gabriel Weinberg's Mental Models I Find Repeatedly Useful
James Clear Mental Models Overview
Proxy“A variable that is not in itself directly relevant, but that serves in place of an unobservable or immeasurable variable. In order for a variable to be a good proxy, it must have a close correlation, not necessarily linear, with the variable of interest.” (related: revealed preference; Proxy War — “A conflict between two nations where neither country directly engages the other.”)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Selection Bias “The selection of individuals, groups or data for analysis in such a way that proper randomization is not achieved, thereby ensuring that the sample obtained is not representative of the population intended to be analyzed.” (related: sampling bias)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Response Bias“A wide range of cognitive biases that influence the responses of participants away from an accurate or truthful response.”Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Observer Effect“Changes that the act of observation will make on a phenomenon being observed.” (related: Schrödinger’s cat)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Systems Thinking “By taking the overall system as well as its parts into account systems thinking is designed to avoid potentially contributing to further development of unintended consequences.” (related: causal loop diagrams; stock and flow; Le Chatelier’s principle, hysteresis — “the time-based dependence of a system’s output on present and past inputs.”; “Can’t see the forest for the trees.”)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Scenario Analysis “A process of analyzing possible future events by considering alternative possible outcomes.” (related: “Skate to where the puck is going.”; black swan theory — “a metaphor that describes an event that comes as a surprise, has a major effect, and is often inappropriately rationalized after the fact with the benefit of hindsight.”)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Normal Distribution“A very common continuous probability distribution…Physical quantities that are expected to be the sum of many independent processes (such as measurement errors) often have distributions that are nearly normal.” (related: central limit theorem)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Sensitivity Analysis“The study of how the uncertainty in the output of a mathematical model or system (numerical or otherwise) can be apportioned to different sources of uncertainty in its inputs.”Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Cost-benefit Analysis“A systematic approach to estimating the strengths and weaknesses of alternatives that satisfy transactions, activities or functional requirements for a business.” (related: net present value — “a measurement of the profitability of an undertaking that is calculated by subtracting the present values of cash outflows (including initial cost) from the present values of cash inflows over a period of time.”, discount rate)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Simulation “The imitation of the operation of a real-world process or system over time.” (related: Queuing theory — “the mathematical study of waiting lines, or queues.”)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Pareto Efficiency “A state of allocation of resources in which it is impossible to make any one individual better off without making at least one individual worse off…A Pareto improvement is defined to be a change to a different allocation that makes at least one individual better off without making any other individual worse off, given a certain initial allocation of goods among a set of individuals.”Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
NumeracyPermutations and CombinationsThe mathematics of permutations and combinations leads us to understand the practical probabilities of the world around us, how things can be ordered, and how we should think about things.Shane Parrish's Farnam Street Mental Model Guide11
Algebraic EquivalenceThe introduction of algebra allowed us to demonstrate mathematically and abstractly that two seemingly different things could be the same. By manipulating symbols, we can demonstrate equivalence or inequivalence, the use of which led humanity to untold engineering and technical abilities. Knowing at least the basics of algebra can allow us to understand a variety of important results.Shane Parrish's Farnam Street Mental Model Guide11
RandomnessThough the human brain has trouble comprehending it, much of the world is composed of random, non-sequential, non-ordered events. We are “fooled” by random effects when we attribute causality to things that are actually outside of our control. If we don’t course-correct for this fooled-by-randomness effect – our faulty sense of pattern-seeking – we will tend to see things as being more predictable than they are and act accordingly.Shane Parrish's Farnam Street Mental Model Guide11
Stochastic Processes (Poisson, Markov, Random Walk)A stochastic process is a random statistical process and encompasses a wide variety of processes in which the movement of an individual variable can be impossible to predict but can be thought through probabilistically. The wide variety of stochastic methods helps us describe systems of variables through probabilities without necessarily being able to determine the position of any individual variable over time. For example, it’s not possible to predict stock prices on a day-to-day basis, but we can describe the probability of various distributions of their movements over time. Obviously, it is much more likely that the stock market (a stochastic process) will be up or down 1% in a day than up or down 10%, even though we can’t predict what tomorrow will bring.Shane Parrish's Farnam Street Mental Model Guide11
CompoundingIt’s been said that Einstein called compounding a wonder of the world. He probably didn’t, but it is a wonder. Compounding is the process by which we add interest to a fixed sum, which then earns interest on the previous sum and the newly added interest, and then earns interest on that amount, and so on ad infinitum. It is an exponential effect, rather than a linear, or additive, effect. Money is not the only thing that compounds; ideas and relationships do as well. In tangible realms, compounding is always subject to physical limits and diminishing returns; intangibles can compound more freely. Compounding also leads to the time value of money, which underlies all of modern finance. - Shane Parrish

“Interest on interest. It is the result of reinvesting interest, rather than paying it out, so that interest in the next period is then earned on the principal sum plus previously-accumulated interest.” - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
Multiplying by ZeroAny reasonably educated person knows that any number multiplied by zero, no matter how large the number, is still zero. This is true in human systems as well as mathematical ones. In some systems, a failure in one area can negate great effort in all other areas. As simple multiplication would show, fixing the “zero” often has a much greater effect than does trying to enlarge the other areas.Shane Parrish's Farnam Street Mental Model Guide11
ChurnInsurance companies and subscription services are well aware of the concept of churn – every year, a certain number of customers are lost and must be replaced. Standing still is the equivalent of losing, as seen in the model called the “Red Queen Effect.” Churn is present in many business and human systems: A constant figure is periodically lost and must be replaced before any new figures are added over the top.Shane Parrish's Farnam Street Mental Model Guide11
Law of Large NumbersOne of the fundamental underlying assumptions of probability is that as more instances of an event occur, the actual results will converge on the expected ones. For example, if I know that the average man is 5 feet 10 inches tall, I am far more likely to get an average of 5′10″ by selecting 500 men at random than 5 men at random. The opposite of this model is the law of small numbers, which states that small samples can and should be looked at with great skepticism.Shane Parrish's Farnam Street Mental Model Guide11
Bell Curve/Normal DistributionThe normal distribution is a statistical process that leads to the well-known graphical representation of a bell curve, with a meaningful central “average” and increasingly rare standard deviations from that average when correctly sampled. (The so-called “central limit” theorem.) Well-known examples include human height and weight, but it’s just as important to note that many common processes, especially in non-tangible systems like social systems, do not follow the normal distribution.Shane Parrish's Farnam Street Mental Model Guide11
Power LawsOne of the most common processes that does not fit the normal distribution is that of a power law, whereby one quantity varies with another’s exponent rather than linearly. For example, the Richter scale describes the power of earthquakes on a power-law distribution scale: an 8 is 10x more destructive than a 7, and a 9 is 10x more destructive than an 8. The central limit theorem does not apply and there is thus no “average” earthquake. This is true of all power-law distributions. - Shane Parrish

“A functional relationship between two quantities, where a relative change in one quantity results in a proportional relative change in the other quantity, independent of the initial size of those quantities: one quantity varies as a power of another.” (related: Pareto distribution; Pareto principle — “for many events, roughly 80% of the effects come from 20% of the causes.”, diminishing returns, premature optimization, heavy-tailed distribution, fat-tailed distribution; long tail — “the portion of the distribution having a large number of occurrences far from the “head” or central part of the distribution.”; black swan theory — “a metaphor that describes an event that comes as a surprise, has a major effect, and is often inappropriately rationalized after the fact with the benefit of hindsight.”) - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
Fat-Tailed Processes (Extremistan)A process can often look like a normal distribution but have a large “tail” – meaning that seemingly outlier events are far more likely than they are in an actual normal distribution. A strategy or process may be far more risky than a normal distribution is capable of describing if the fat tail is on the negative side, or far more profitable if the fat tail is on the positive side. Much of the human social world is said to be fat-tailed rather than normally distributed.Shane Parrish's Farnam Street Mental Model Guide11
Bayesian UpdatingThe Bayesian method is a method of thought (named for Thomas Bayes) whereby one takes into account all prior relevant probabilities and then incrementally updates them as newer information arrives. This method is especially productive given the fundamentally non-deterministic world we experience: We must use prior odds and new information in combination to arrive at our best decisions. This is not necessarily our intuitive decision-making engine.Shane Parrish's Farnam Street Mental Model Guide11
Regression to the MeanIn a normally distributed system, long deviations from the average will tend to return to that average with an increasing number of observations: the so-called Law of Large Numbers. We are often fooled by regression to the mean, as with a sick patient improving spontaneously around the same time they begin taking an herbal remedy, or a poorly performing sports team going on a winning streak. We must be careful not to confuse statistically likely events with causal ones. - Shane Parrish

“The phenomenon that if a variable is extreme on its first measurement, it will tend to be closer to the average on its second measurement.” (related: Pendulum swing; variance; Gambler’s fallacy) - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
Order of MagnitudeIn many, perhaps most, systems, quantitative description down to a precise figure is either impossible or useless (or both). For example, estimating the distance between our galaxy and the next one over is a matter of knowing not the precise number of miles, but how many zeroes are after the 1. Is the distance about 1 million miles or about 1 billion? This thought habit can help us escape useless precision. - Shane Parrish

“An order-of-magnitude estimate of a variable whose precise value is unknown is an estimate rounded to the nearest power of ten.” (related: order of approximation, back-of-the-envelope calculation, dimensional analysis, Fermi problem) - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
SystemsScaleOne of the most important principles of systems is that they are sensitive to scale. Properties (or behaviors) tend to change when you scale them up or down. In studying complex systems, we must always be roughly quantifying – in orders of magnitude, at least – the scale at which we are observing, analyzing, or predicting the system.Shane Parrish's Farnam Street Mental Model Guide11
Diminishing Returns"Related to scale, most important real-world results are subject to an eventual decrease of incremental value. A good example would be a poor family: Give them enough money to thrive, and they are no longer poor. But after a certain point, additional money will not improve their lot; there is a clear diminishing return of additional dollars at some roughly quantifiable point. Often, the law of diminishing returns veers into negative territory – i.e., receiving too much money could destroy the poor family." —Shane Parrish


"When you focus on improving the same product area, the amount of customer value created over time will diminish for every unit of effort.

How it’s useful

Assuming you are effectively iterating the product based on customer feedback and research, you will eventually hit a point where there’s just not that much you can do to make it better. It’s time for your team to move on and invest in something new."
— Brandon Chu
Shane Parrish's Farnam Street Mental Model Guide -


Product Management Mental Models for Everyone -
Product Management Mental Models for Everyone
Pareto Principle (80/20 Rule)Named for Italian polymath Vilfredo Pareto, who noticed that 80% of Italy’s land was owned by about 20% of its population, the Pareto Principle states that a small amount of some phenomenon causes a disproportionately large effect. The Pareto Principle is an example of a power-law type of statistical distribution – as distinguished from a traditional bell curve – and is demonstrated in various phenomena ranging from wealth to city populations to important human habits.Shane Parrish's Farnam Street Mental Model Guide11
Feedback Loops (and Homeostasis)All complex systems are subject to positive and negative feedback loops whereby A causes B, which in turn influences A (and C), and so on – with higher-order effects frequently resulting from continual movement of the loop. In a homeostatic system, a change in A is often brought back into line by an opposite change in B to maintain the balance of the system, as with the temperature of the human body or the behavior of an organizational culture. Automatic feedback loops maintain a “static” environment unless and until an outside force changes the loop. A “runaway feedback loop” describes a situation in which the output of a reaction becomes its own catalyst (auto-catalysis).Shane Parrish's Farnam Street Mental Model Guide11
Chaos Dynamics (Sensitivity to Initial Conditions or Butterfly Effect)In a world such as ours, governed by chaos dynamics, small changes (perturbations) in initial conditions have massive downstream effects as near-infinite feedback loops occur; this phenomenon is also called the butterfly effect. This means that some aspects of physical systems (like the weather more than a few days from now) as well as social systems (the behavior of a group of human beings over a long period) are fundamentally unpredictable.Shane Parrish's Farnam Street Mental Model Guide11
Preferential Attachment (Cumulative Advantage)A preferential attachment situation occurs when the current leader is given more of the reward than the laggards, thereby tending to preserve or enhance the status of the leader. A strong network effect is a good example of preferential attachment; a market with 10x more buyers and sellers than the next largest market will tend to have a preferential attachment dynamic.Shane Parrish's Farnam Street Mental Model Guide11
EmergenceHigher-level behavior tends to emerge from the interaction of lower-order components. The result is frequently not linear – not a matter of simple addition – but rather non-linear, or exponential. An important resulting property of emergent behavior is that it cannot be predicted from simply studying the component parts. - Shane Parrish

“Whereby larger entities, patterns, and regularities arise through interactions among smaller or simpler entities that themselves do not exhibit such properties.” (related: decentralized system, spontaneous order) - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
IrreducibilityWe find that in most systems there are irreducible quantitative properties, such as complexity, minimums, time, and length. Below the irreducible level, the desired result simply does not occur. One cannot get several women pregnant to reduce the amount of time needed to have one child, and one cannot reduce a successfully built automobile to a single part. These results are, to a defined point, irreducible.Shane Parrish's Farnam Street Mental Model Guide11
Tragedy of the CommonsA concept introduced by the economist and ecologist Garrett Hardin, the Tragedy of the Commons states that in a system where a common resource is shared, with no individual responsible for the wellbeing of the resource, it will tend to be depleted over time. The Tragedy is reducible to incentives: Unless people collaborate, each individual derives more personal benefit than the cost that he or she incurs, and therefore depletes the resource for fear of missing out.Shane Parrish's Farnam Street Mental Model Guide11
Gresham’s LawGresham’s Law, named for the financier Thomas Gresham, states that in a system of circulating currency, forged currency will tend to drive out real currency, as real currency is hoarded and forged currency is spent. We see a similar result in human systems, as with bad behavior driving out good behavior in a crumbling moral system, or bad practices driving out good practices in a crumbling economic system. Generally, regulation and oversight are required to prevent results that follow Gresham’s Law.Shane Parrish's Farnam Street Mental Model Guide11
Algorithms"While hard to precisely define, an algorithm is generally an automated set of rules or a “blueprint” leading a series of steps or actions resulting in a desired outcome, and often stated in the form of a series of “If → Then” statements. Algorithms are best known for their use in modern computing, but are a feature of biological life as well. For example, human DNA contains an algorithm for building a human being." - Shane Parrish

An algorithm is a certain sort of formal process that can be counted on—logically—to yield a certain sort of result whenever it is “run” or instantiated. Algorithms are not new, and they were not new in Darwin’s day.
The idea that an algorithm is a foolproof and somehow “mechanical” procedure has been present for centuries, but it was the pioneering work of Alan Turing, Kurt Gödel, and Alonzo Church in the 1930s that more or less fixed our current understanding of the term. Three key features of algorithms will be important to us, and each is somewhat difficult to define.
(1) Substrate neutrality
(2) Underlying mindlessness
(3) Guaranteed results
- Daniel Dennett
Shane Parrish's Farnam Street Mental Model Guide

Philosopher Daniel Dennett's Book Intuition Pumps
Fragility – Robustness – AntifragilityPopularized by Nassim Taleb, the sliding scale of fragility, robustness, and antifragility refers to the responsiveness of a system to incremental negative variability. A fragile system or object is one in which additional negative variability has a disproportionately negative impact, as with a coffee cup shattering from a 6-foot fall, but receiving no damage at all (rather than 1/6th of the damage) from a 1-foot fall. A robust system or object tends to be neutral to the additional negativity variability, and of course, an antifragile system benefits: If there were a cup that got stronger when dropped from 6 feet than when dropped from 1 foot, it would be termed antifragile.Shane Parrish's Farnam Street Mental Model Guide11
Backup Systems/Redundancy"A critical model of the engineering profession is that of backup systems. A good engineer never assumes the perfect reliability of the components of the system. He or she builds in redundancy to protect the integrity of the total system. Without the application of this robustness principle, tangible and intangible systems tend to fail over time." - Shane Parrish

"In reliability engineering, redundancy is defined as the existence of more than one means for accomplishing a given task. Thus all of these means must fail before there is a system failure.
A Backup System is turning a Multiplicative System with a single break point into an additive system with two or more break points.
How to use this mental model: Analyze the primary system
- Is the primary system a multiplicative one or additive one ? If the system if additive, by definition it doesn't need a backup system.
if the primary system is a simple or complex one ? If the system is a simple one, other means of increasing reliability could be more effective( margin of safety )
- Designing Backup System.
if the primary system is a complex and multiplicative one, adding backup system could greatly improve reliability." - James Clear
Shane Parrish's Farnam Street Mental Model Guide

James Clear Mental Models Overview,backup_systemredundancy.html
Margin of Safety"Similarly, engineers have also developed the habit of adding a margin for error into all calculations. In an unknown world, driving a 9,500-pound bus over a bridge built to hold precisely 9,600 pounds is rarely seen as intelligent. Thus, on the whole, few modern bridges ever fail. In practical life outside of physical engineering, we can often profitably give ourselves margins as robust as the bridge system." -Shane Parrish

“The difference between the intrinsic value of a stock and its market price.” - Gabriel Weinberg

"This term, margin of safety, is an engineering concept used to describe the ability of a system to withstand loads that are greater than expected.
There are many ways to implement a margin of safety in everyday life. The core idea is to protect yourself from unforeseen problems and challenges by building a buffer between what you expect to happen and what could happen. This idea is widely useful on a day-to-day basis because uncertainty creeps into every area of life. Let's explore a few ways we can use this concept to live better." - James Clear
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful

James Clear Mental Models Overview
CriticalityA system becomes critical when it is about to jump discretely from one phase to another. The marginal utility of the last unit before the phase change is wildly higher than any unit before it. A frequently cited example is water turning from a liquid to a vapor when heated to a specific temperature. “Critical mass” refers to the mass needed to have the critical event occur, most commonly in a nuclear system.Shane Parrish's Farnam Street Mental Model Guide11
Network Effects"A network tends to become more valuable as nodes are added to the network: this is known as the network effect. An easy example is contrasting the development of the electricity system and the telephone system. If only one house has electricity, its inhabitants have gained immense value, but if only one house has a telephone, its inhabitants have gained nothing of use. Only with additional telephones does the phone network gain value. This network effect is widespread in the modern world and creates immense value for organizations and customers alike." - Shane Parrish

"Network effects occur when a product or service becomes more valuable as more people use it. Network effects help you build better, faster-growing and more valuable products and businesses." -  Robert Metcalfe

“The effect that one user of a good or service has on the value of that product to other people. When a network effect is present, the value of a product or service is dependent on the number of others using it.” - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

 Robert Metcalfe via 13 Mental Models Every Founder Should Know

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
Black SwanAlso popularized by Nassim Taleb, a Black Swan is a rare and highly consequential event that is invisible to a given observer ahead of time. It is a result of applied epistemology: If you have seen only white swans, you cannot categorically state that there are no black swans, but the inverse is not true: seeing one black swan is enough for you to state that there are black swans. Black Swan events are necessarily unpredictable to the observer (as Taleb likes to say, Thanksgiving is a Black Swan for the turkey, not the butcher) and thus must be dealt with by addressing the fragility-robustness-antifragility spectrum rather than through better methods of prediction.Shane Parrish's Farnam Street Mental Model Guide11
Via Negativa – Omission/Removal/Avoidance of HarmIn many systems, improvement is at best, or at times only, a result of removing bad elements rather than of adding good elements. This is a credo built into the modern medical profession: First, do no harm. Similarly, if one has a group of children behaving badly, removal of the instigator is often much more effective than any form of punishment meted out to the whole group.Shane Parrish's Farnam Street Mental Model Guide11
The Lindy EffectThe Lindy Effect refers to the life expectancy of a non-perishable object or idea being related to its current lifespan. If an idea or object has lasted for X number of years, it would be expected (on average) to last another X years. Although a human being who is 90 and lives to 95 does not add 5 years to his or her life expectancy, non-perishables lengthen their life expectancy as they continually survive. A classic text is a prime example: if humanity has been reading Shakespeare’s plays for 500 years, it will be expected to read them for another 500.Shane Parrish's Farnam Street Mental Model Guide11
Renormalization GroupThe renormalization group technique allows us to think about physical and social systems at different scales. An idea from physics, and a complicated one at that, the application of a renormalization group to social systems allows us to understand why a small number of stubborn individuals can have a disproportionate impact if those around them follow suit on increasingly large scales.Shane Parrish's Farnam Street Mental Model Guide11
Spring-loadingA system is spring-loaded if it is coiled in a certain direction, positive or negative. Positively spring-loading systems and relationships is important in a fundamentally unpredictable world to help protect us against negative events. The reverse can be very destructive.Shane Parrish's Farnam Street Mental Model Guide11
Complex Adaptive SystemsA complex adaptive system, as distinguished from a complex system in general, is one that can understand itself and change based on that understanding. Complex adaptive systems are social systems. The difference is best illustrated by thinking about weather prediction contrasted to stock market prediction. The weather will not change based on an important forecaster’s opinion, but the stock market might. Complex adaptive systems are thus fundamentally not predictable.Shane Parrish's Farnam Street Mental Model Guide11
PhysicsLaws of ThermodynamicsThe laws of thermodynamics describe energy in a closed system. The laws cannot be escaped and underlie the physical world. They describe a world in which useful energy is constantly being lost, and energy cannot be created or destroyed. Applying their lessons to the social world can be a profitable enterprise.Shane Parrish's Farnam Street Mental Model Guide11
Reciprocity"If I push on a wall, physics tells me that the wall pushes back with equivalent force. In a biological system, if one individual acts on another, the action will tend to be reciprocated in kind. And of course, human beings act with intense reciprocity demonstrated as well." - Shane Parrish

"The norm of reciprocity requires that we repay in kind what another has done for us. It can be understood as the expectation that people will respond favorably to each other by returning benefits for benefits, and responding with either indifference or hostility to harms. The social norm of reciprocity often takes different forms in different areas of social life, or in different societies. All of them, however, are distinct from related ideas such as gratitude, the Golden Rule, or mutual goodwill. See reciprocity (social and political philosophy) for an analysis of the concepts involved. The norm of reciprocity mirrors the concept of reciprocal altruism in evolutionary biology. However, evolutionary theory and therefore sociobiology was not well received by mainstream psychologists. This led to the revitalisation of reciprocal altruism underneath the new social psychological concept, norm of reciprocity. Reciprocal altruism has been applied to various species, including humans, while mainstream psychologists use the norm of reciprocity to only explain humans." - Wikipedia (James Clear)
Shane Parrish's Farnam Street Mental Model Guide

James Clear Mental Models Overview
Velocity"Velocity is not equivalent to speed; the two are sometimes confused. Velocity is speed plus vector: how fast something gets somewhere. An object that moves two steps forward and then two steps back has moved at a certain speed but shows no velocity. The addition of the vector, that critical distinction, is what we should consider in practical life." - Shane Parrish

"The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of its speed and direction of motion (e.g. 60 km/h to the north). Velocity is an important concept in kinematics, the branch of classical mechanics that describes the motion of bodies.

Velocity is a physical vector quantity; both magnitude and direction are needed to define it." - Wikipedia (James Clear)
Shane Parrish's Farnam Street Mental Model Guide

James Clear Mental Models Overview
Relativity"Relativity has been used in several contexts in the world of physics, but the important aspect to study is the idea that an observer cannot truly understand a system of which he himself is a part. For example, a man inside an airplane does not feel like he is experiencing movement, but an outside observer can see that movement is occurring. This form of relativity tends to affect social systems in a similar way." - Shane Parrish

"The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity.Special relativity applies to elementary particles and their interactions, describing all their physical phenomena except gravity. General relativity explains the law of gravitation and its relation to other forces of nature. It applies to the cosmological and astrophysical realm, including astronomy." - Wikipedia (James Clear)
Shane Parrish's Farnam Street Mental Model Guide

James Clear Mental Models Overview
Activation Energy"A fire is not much more than a combination of carbon and oxygen, but the forests and coal mines of the world are not combusting at will because such a chemical reaction requires the input of a critical level of “activation energy” in order to get a reaction started. Two combustible elements alone are not enough." - Shane Parrish

“The minimum energy which must be available to a chemical system with potential reactants to result in a chemical reaction.” - Gabriel Weinberg

"In chemistry, activation energy is the energy which must be available to a chemical system with potential reactants to result in a chemical reaction.[1] Activation energy may also be defined as the minimum energy required to start a chemical reaction. The activation energy of a reaction is usually denoted by Ea and given in units of kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).

Activation energy can be thought of as the height of the potential barrier (sometimes called the energy barrier) separating two minima of potential energy (of the reactants and products of a reaction). For a chemical reaction to proceed at a reasonable rate, there should exist an appreciable number of molecules with translational energy equal to or greater than the activation energy." - Wikipedia (James Clear )
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful"

James Clear Mental Models Overview
CatalystsA catalyst either kick-starts or maintains a chemical reaction, but isn’t itself a reactant. The reaction may slow or stop without the addition of catalysts. Social systems, of course, take on many similar traits, and we can view catalysts in a similar light. - Shane Parrish

"Catalysis (/kəˈtælɪsɪs/) is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst, which is not consumed in the catalyzed reaction and can continue to act repeatedly. Often only tiny amounts of catalyst are required in principle.

In general, reactions occur faster with a catalyst because they require less activation energy. In catalyzed mechanisms, the catalyst usually reacts to form a temporary intermediate which then regenerates the original catalyst in a cyclic process." - Wikipedia (Gabriel Weinberg)

“A substance which increases the rate of a chemical reaction.” (related: tipping point) - James Clear
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful

James Clear Mental Models Overview
Leverage"Most of the engineering marvels of the world have been accomplished with applied leverage. As famously stated by Archimedes, “Give me a lever long enough and I shall move the world.” With a small amount of input force, we can make a great output force through leverage. Understanding where we can apply this model to the human world can be a source of great success." - Shane Parrish

“The force amplification achieved by using a tool, mechanical device or machine system.” (related: Theory of constraints — “a management paradigm that views any manageable system as being limited in achieving more of its goals by a very small number of constraints.” - Gabriel Weinberg

Math & Engineering: "Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force. The model for this is the law of the lever. Machine components designed to manage forces and movement in this way are called mechanisms.An ideal mechanism transmits power without adding to or subtracting from it. This means the ideal mechanism does not include a power source, is frictionless, and is constructed from rigid bodies that do not deflect or wear. The performance of a real system relative to this ideal is expressed in terms of efficiency factors that take into account departures from the ideal." - Wikipedia (James Clear)
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful"

James Clear Mental Models Overview
Inertia"An object in motion with a certain vector wants to continue moving in that direction unless acted upon. This is a fundamental physical principle of motion; however, individuals, systems, and organizations display the same effect. It allows them to minimize the use of energy, but can cause them to be destroyed or eroded." - Shane Parrish

"the resistance of any physical object to any change in its state of motion; this includes changes to its speed, direction or state of rest. It is the tendency of objects to keep moving in a straight line at constant velocity.” (related: strategy tax — “sometimes products developed inside a company…have to accept constraints that go against competitiveness, or might displease users, in order to further the cause of another product.”; flywheel — “a rotating mechanical device that is used to store rotational energy. Flywheels have an inertia called the moment of inertia and thus resist changes in rotational speed.”) - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful"
AlloyingWhen we combine various elements, we create new substances. This is no great surprise, but what can be surprising in the alloying process is that 2+2 can equal not 4 but 6 – the alloy can be far stronger than the simple addition of the underlying elements would lead us to believe. This process leads us to engineering great physical objects, but we understand many intangibles in the same way; a combination of the right elements in social systems or even individuals can create a 2+2=6 effect similar to alloying.Shane Parrish's Farnam Street Mental Model Guide11
Critical Mass “The smallest amount of fissile material needed for a sustained nuclear chain reaction.” “In social dynamics, critical mass is a sufficient number of adopters of an innovation in a social system so that the rate of adoption becomes self-sustaining and creates further growth.” - Gabriel Weinberg

"A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature, and its surroundings. The concept is important in nuclear weapon design." - Wikipedia (James Clear)
Gabriel Weinberg's Mental Models I Find Repeatedly Useful
James Clear Mental Models Overview"
Half-life“the time required for a quantity to reduce to half its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay.” (related: viral marketing)Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Heisenberg Uncertainty Principle “A fundamental limit to the precision with which certain pairs of physical properties of a particle, known as complementary variables, such as position x and momentum p, can be known.”Gabriel Weinberg's Mental Models I Find Repeatedly Useful11
Biological WorldIncentivesAll creatures respond to incentives to keep themselves alive. This is the basic insight of biology. Constant incentives will tend to cause a biological entity to have constant behavior, to an extent. Humans are included and are particularly great examples of the incentive-driven nature of biology; however, humans are complicated in that their incentives can be hidden or intangible. The rule of life is to repeat what works and has been rewarded. - Shane Parrish

Negotiating: “Something that motivates an individual to perform an action.” (related: carrot and stick — “a policy of offering a combination of rewards and punishment to induce behavior.”) - Gabriel Weinberg

Business - Economics: "An incentive is something that motivates an individual to perform an action. The study of incentive structures is central to the study of all economic activities (both in terms of individual decision-making and in terms of co-operation and competition within a larger institutional structure). Economic analysis, then, of the differences between societies (and between different organizations within a society) largely amounts to characterizing the differences in incentive structures faced by individuals involved in these collective efforts. Ultimately, incentives aim to provide value for money and contribute to organizational success. As such the design of incentive systems is a key management activity." - Wikipedia (James Clear)
Shane Parrish's Farnam Street Mental Model Guide

Gabriel Weinberg's Mental Models I Find Repeatedly Useful"

James Clear Mental Models Overview
Cooperation (Including Symbiosis)Competition tends to describe most biological systems, but cooperation at various levels is just as important a dynamic. In fact, the cooperation of a bacterium and a simple cell probably created the first complex cell and all of the life we see around us. Without cooperation, no group survives, and the cooperation of groups gives rise to even more complex versions of organization. Cooperation and competition tend to coexist at multiple levels.Shane Parrish's Farnam Street Mental Model Guide11
Tendency to Minimize Energy Output (Mental & Physical)In a physical world governed by thermodynamics and competition for limited energy and resources, any biological organism that was wasteful with energy would be at a severe disadvantage for survival. Thus, we see in most instances that behavior is governed by a tendency to minimize energy usage when at all possible.Shane Parrish's Farnam Street Mental Model Guide11
AdaptationSpecies tend to adapt to their surroundings in order to survive, given the combination of their genetics and their environment – an always-unavoidable combination. However, adaptations made in an individual's lifetime are not passed down genetically, as was once thought: Populations of species adapt through the process of evolution by natural selection, as the most-fit examples of the species replicate at an above-average rate.Shane Parrish's Farnam Street Mental Model Guide11
Evolution by Natural SelectionEvolution by natural selection was once called “the greatest idea anyone ever had.” In the 19th century, Charles Darwin and Alfred Russel Wallace simultaneous realized that species evolve through random mutation and differential survival rates. If we call human intervention in animal-breeding an example of “artificial selection,” we can call Mother Nature deciding the success or failure of a particular mutation “natural selection.” Those best suited for survival tend to be preserved. But of course, conditions change. - Shane Parrish

"Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in heritable traits of a population over time. Charles Darwin popularised the term "natural selection", and compared it with artificial selection...Natural selection acts on the phenotype, or the observable characteristics of an organism, but the genetic (heritable) basis of any phenotype that gives a reproductive advantage may become more common in a population. Over time, this process can result in populations that specialise for particular ecological niches (microevolution) and may eventually result in speciation (the emergence of new species, macroevolution). In other words, natural selection is a key process in the evolution of a population. Natural selection can be contrasted with artificial selection, in which humans intentionally choose specific traits, whereas in natural selection there is no intentional choice." - Wikipedia (James Clear)

“The differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in heritable traits of a population over time.” - Gabriel Weinberg
Shane Parrish's Farnam Street Mental Model Guide

James Clear Mental Models Overview

Gabriel Weinberg's Mental Models I Find Repeatedly Useful
The Red Queen Effect (Co-evolutionary Arms Race)The evolution-by-natural-selection model leads to something of an arms race among species competing for limited resources. When one species evolves an advantageous adaptation, a competing species must respond in kind or fail as a species. Standing pat can mean falling behind. This arms race is called the Red Queen Effect for the character in Alice in Wonderland who said, “Now, here, you see, it takes all the running you can do, to keep in the same place.”Shane Parrish's Farnam Street Mental Model Guide11
ReplicationA fundamental building block of diverse biological life is high-fidelity replication. The fundamental unit of replication seems to be the DNA molecule, which provides a blueprint for the offspring to be built from physical building blocks. There are a variety of replication methods, but most can be lumped into sexual and asexual.Shane Parrish's Farnam Street Mental Model Guide11
Hierarchical and Other Organizing InstinctsMost complex biological organisms have an innate feel for how they should organize. While not all of them end up in hierarchical structures, many do, especially in the animal kingdom. Human beings like to think they are outside of this, but they feel the hierarchical instinct as strongly as any other organism.Shane Parrish's Farnam Street Mental Model Guide11
Self-Preservation InstinctsWithout a strong self-preservation instinct in an organism’s DNA, it would tend to disappear over time, thus eliminating that DNA. While cooperation is another important model, the self-preservation instinct is strong in all organisms and can cause violent, erratic, and/or destructive behavior for those around them.Shane Parrish's Farnam Street Mental Model Guide11
Simple Physiological Reward-SeekingAll organisms feel pleasure and pain from simple chemical processes in their bodies which respond predictably to the outside world. Reward-seeking is an effective survival-promoting technique on average. However, those same pleasure receptors can be co-opted to cause destructive behavior, as with drug abuse.Shane Parrish's Farnam Street Mental Model Guide11
ExaptationIntroduced by the biologist Steven Jay Gould, an exaptation refers to a trait developed for one purpose that is later used for another purpose. This is one way to explain the development of complex biological features like an eyeball; in a more primitive form, it may have been used for something else. Once it was there, and once it developed further, 3D sight became possible.Shane Parrish's Farnam Street Mental Model Guide11
ExtinctionThe inability to survive can cause an extinction event, whereby an entire species ceases to compete and replicate effectively. Once its numbers have dwindled to a critically low level, an extinction can be unavoidable (and predictable) given the inability to effectively replicate in large enough numbers.Shane Parrish's Farnam Street Mental Model Guide11