The Open Curriculum

The Mind · Level 2

The Great Mental Models, Vols. 1–4

Shane Parrish, Rhiannon Beaubien and Rosie Leizrowice · 2019–2024

Thesis

Better decisions come less from knowing more facts than from carrying the most durable ideas of many disciplines, from general thinking and the sciences to systems, mathematics, economics and art, applying them outside the field they came from, and knowing where each one stops applying.

The main ideas

Maps, circles and first principles

The first volume, General Thinking Concepts (2019), starts with Alfred Korzybski's line that the map is not the territory. Every model reduces reality, and the reduction is the point: the London Underground map is ideal for a passenger and useless to a driver. The failure is forgetting the reduction, as when Garrett Hardin's tragedy of the commons is treated as fixed law, a habit Elinor Ostrom warned against, or when planners redesigned neighbourhoods from maps that left out how people used the streets, which Jane Jacobs criticized.

The circle of competence, from Warren Buffett and Charlie Munger, is the area where you know the terrain. What matters is knowing where it ends: a Sherpa guide such as Tenzing Norgay knows Everest's weather and routes, while a client who has read about it knows the vocabulary.

First principles thinking separates what is known to be true from what is assumed, using Socratic questioning or repeated "why" questions. The book's case is the medical belief that bacteria could not survive in the stomach, so ulcers were blamed on stress, until Robin Warren and Barry Marshall showed that the bacterium Helicobacter pylori caused most of them. Thought experiments extend the method to tests that cannot be run, from Einstein's reasoning about relativity to John Rawls's veil of ignorance.

Implication: before relying on a model, a report or your own judgment, ask what it was built for, whether the problem is inside your circle, and which constraints are facts rather than habits.

Consequences, odds and inversion

Second-order thinking asks what the result of an action causes in turn. Feeding antibiotics to livestock makes animals grow fatter, the first-order effect, and breeds resistant bacteria that reach the food supply, the second. Probabilistic thinking replaces "what will happen" with how likely each outcome is: updating beliefs in proportion to new evidence, as Bayes's rule prescribes, and recognizing fat-tailed distributions, where extreme events are far more common than a normal curve implies. The book's case is Vera Atkins of Britain's Special Operations Executive, deciding which agents to send into occupied France on incomplete information.

Inversion, from the mathematician Carl Jacobi's advice to "invert, always invert," asks what would guarantee failure, or what conditions would make a goal inevitable. Edward Bernays, hired to sell cigarettes to women, asked what world would make women's smoking normal and created it, staging the "torches of freedom" at New York's Easter parade in 1929.

Two razors close the volume. Occam's razor prefers the explanation with fewer assumptions; Vera Rubin's measurements of galaxy rotation made unseen dark matter the simplest account of the data. Hanlon's razor holds that error explains more than malice. Vasili Arkhipov, an officer aboard a Soviet submarine in the Cuban Missile Crisis, refused to approve a nuclear torpedo launch when practice depth charges were taken for an attack.

Implication: for any decision, ask "and then what?" at least twice, write down what would make it fail, and check whether a simpler explanation fits before acting on a sinister one.

Forces and reactions

The second volume, Physics, Chemistry and Biology (2019), borrows from the hard sciences. Relativity says that what an observer sees depends on where they stand: Galileo's scientist below decks on a moving ship cannot tell from a dropped ball that the ship is moving. Velocity is speed with a direction: activity without direction produces no progress. Inertia means that a moving body keeps moving, which is why established momentum, such as a successful company's habits, is hard to change. Leverage multiplies force, the principle behind Archimedes's boast that with a place to stand he could move the earth.

From chemistry, activation energy is the energy needed to start a reaction: a match must be struck, and a fire needs paper and kindling before it can burn logs. A catalyst speeds a reaction without being consumed by it. The Black Death acted as one on European society: by killing so many workers, it created a labour shortage that raised wages. Alloying combines elements into a material with properties neither has alone, as in partnerships such as Steve Jobs and Steve Wozniak at Apple.

Implication: to start a change, identify the activation energy it needs and supply it; to sustain one, build momentum and point it in a direction. Look for combinations of people or skills that produce what neither could alone.

Life's rules

Biology contributes the models of competition. Natural selection removes what does not fit its environment; the passenger pigeon ended with the death of the last one, Martha, in 1914. The Red Queen effect, named for Lewis Carroll's character who must run to stay in place, holds that competitors adapt to each other, so standing still means falling behind.

An ecosystem is a web in which removing one species changes the rest. Sea otters eat urchins, and urchins eat kelp; where otters disappear, urchins multiply and kelp forests collapse. Niches separate generalists, who survive change by doing many things adequately, from specialists, who do one thing very well and depend on the conditions for it. Cooperation produced the complex cell: mitochondria began as bacteria living inside another cell.

Incentives explain behaviour across both: in the thalidomide case, money and incentives overrode safety. The tendency to minimize energy output means organisms, people included, default to the least costly response, which is why habits and heuristics persist.

Implication: in any competitive setting, assume rivals are adapting; ask what niche you occupy and what would remove it; and before blaming character, look at the incentives and the energy the right behaviour costs.

Systems

The third volume, Systems and Mathematics (2021), by Rhiannon Beaubien and Rosie Leizrowice, starts with feedback loops. A balancing loop, like a thermostat, holds a system steady; a reinforcing loop amplifies itself, as when paying kidnappers makes future kidnappings more profitable.

A bottleneck is the slowest part of a system, and it sets the pace of the whole. Bottlenecks also drive invention: when the Second World War cut the United States off from supplies controlled by Japan, the shortage pushed the development of nylon and synthetic rubber. Scale changes systems, creating problems that did not exist when they were smaller. A margin of safety is the buffer between what a system is expected to face and what it can survive; engineers design a bridge for the crowd after a sports match, or the population a decade on, not for an average day.

Churn, the steady replacement of parts, keeps systems healthy; Synanon, an organization that tried to stop people leaving, slid into coercion and violence. An algorithm is a repeatable process that turns inputs into outputs: in the 1920s, Bayer tested compounds systematically against deadly bacteria, and the process produced the first broad-spectrum antibacterial drug in 1932. Critical mass is the point at which a change becomes self-sustaining.

Implication: find the bottleneck before improving anything else, build in a margin for the extremes rather than the average, and watch for reinforcing loops you are feeding without meaning to.

Mathematics

Compounding is growth on growth: $100 at 10 percent becomes $110, then $121, and the curve steepens with time. The same applies to skills and knowledge, where each gain makes the next one easier. Sampling warns that conclusions depend on what was examined: someone who has only seen local ponds concludes that all swans are white, until a wider sample finds black swans.

Randomness produces patterns people mistake for design. During the German bombing of London in the Second World War, residents suspected that spies lived in the areas that were spared; the book, following Kahneman, notes that the pattern was random. Regression to the mean is the tendency of extreme results to be followed by more ordinary ones.

Multiplying by zero means a single failure can cancel every strength: a restaurant with excellent service and atmosphere fails if the food is bad. Surface area is how much contact a system has with the outside: circus families that trained only their own children copied each generation from the last, until circus education opened to other disciplines. Global and local maxima distinguish the best result available from the best nearby one: reaching a higher peak can require going downhill first.

Implication: before investing effort in strengths, find the zero that would cancel them; treat streaks and outliers as likely to regress; and when stuck at a local peak, accept a temporary step down to reach a higher one.

Economics and art

The fourth volume, Economics and Art (2024), applies the method to value and attention. Scarcity raises value: Hermès could make more Birkin bags but keeps production below 100,000 a year. Interdependence is the theme of Leonard Read's essay "I, Pencil": no single person knows how to make a pencil, yet markets coordinate the thousands who together do.

Debt brings resources forward from the future, for good or ill. Japan's Meiji government borrowed around 1873 to build banks and railways and repaid the loans. Gresham's law holds that bad money drives out good, as people spend debased coins and hoard sound ones. Bubbles are not only waste: the book presents the Apollo program as a bubble of Cold War prestige, and the 1990s dot-com mania as one that built the internet's infrastructure.

The art models are about reaching people. Audience: the lawyer Clarence Darrow had his clients Leopold and Loeb plead guilty, so that he argued before a judge rather than a jury and could address the judge and public opinion together. Setting: David Byrne argues that music is shaped by the spaces it is written for, from outdoor rhythms to cathedral acoustics to arena rock.

Implication: before pricing, persuading or presenting anything, ask what is scarce, who the audience really is, and what setting the message has to work in.

Limits

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