Pick the kind of situation you are in. You'll see a few thinking tools that might help, where each one comes from, and a question to try.
You have to choose, and the choice matters.
Jeff Bezos's, in his letter with the 2015 annual report. The "around 70% of the information" rule comes from the next year's letter, hedged with "probably", and written about decisions inside a company.
Sources named: Bezos, letters with the 2015 and 2016 annual reports
If this turns out wrong, can you walk back through the door, or not?
Bezos's own account of one decision, in a 2001 interview: "I wanted to project myself forward to age 80". It is one person's way of making one choice.
Sources named: Academy of Achievement interview (4 May 2001)
Picture yourself much older, looking back. Which choice would you regret not making?
The English term is in David I. Green's 1894 paper; the History of Economic Thought website says the doctrine was first introduced "as an all-encompassing theory of cost" in a seminar paper by Friedrich von Wieser (1876). The idea is older: Bastiat's townsman who has spent six francs "cannot spend them on another" thing.
Sources named: Green, QJE (1894); History of Economic Thought website; Bastiat (1850)
If you spend your time or money on this, what can you no longer spend it on?
A Berkshire idea; the earliest use we found is Munger's, in his 1994 talk: "Every person is going to have a circle of competence." Buffett's 1996 letter adds the part people drop: "The size of that circle is not very important; knowing its boundaries, however, is vital."
Sources named: Munger (1994); Buffett, 1996 letter
Is this inside what you know well? Where does that knowledge stop?
Weighing several options? Lay them out in the decision matrix →
Something you are about to start, or are in the middle of.
Gary Klein's, described in Harvard Business Review in September 2007: "team members assume that the project they are planning has just failed". The 30% figure often attached to it could not be checked.
Sources named: Klein, HBR (September 2007)
Imagine the plan has already failed. What went wrong?
The full entry, with sources →Try it in our pre-mortem tool →
Kahneman and Lovallo (1993): "overly optimistic forecasts result from the adoption of an inside view of the problem", paired with a second problem, overly cautious attitudes to risk.
Sources named: Kahneman & Lovallo, Management Science (1993)
Are you judging only from the details of this plan? How did plans like it turn out?
The label is modern, and we found no single origin for it. The idea is stated by Bastiat in 1850: an act or a law produces "not one effect but a series of effects", and only the first is seen.
Sources named: Bastiat, Ce qu'on voit et ce qu'on ne voit pas (1850)
And then what? What follows after the first effect?
Chesterton (The Thing, 1929) says to find out what a fence was for before removing it, and that a reformer who knows may find "they were bad purposes" or ones "no longer served". It is a rule about understanding before change, not against change.
Sources named: Chesterton, "The Drift from Domesticity", The Thing
Before you remove an old rule or step, do you know what it was for?
Someone says something is true, and you want to weigh it.
It began as a rule for interpreting what people mean. Quine (1960) credits the name to N. L. Wilson; his reason: "silliness, beyond a certain point, is less likely than bad translation".
Sources named: Quine, Word and Object (1960); Wilson (1959); Davidson
What is the most sensible reading of what they meant?
Christopher Hitchens, Slate, 20 October 2003: "what can be asserted without evidence can also be dismissed without evidence." It licenses setting a claim aside, not disproving it.
Sources named: Hitchens, Slate (20 October 2003)
Has any evidence been offered? If not, can you set the claim aside for now?
Popularly Carl Sagan's, but the idea runs back through Laplace (1814) to Hume (1748): "A wise man, therefore, proportions his belief to the evidence." Laplace also warned against denying what cannot yet be explained.
Sources named: Hume, Enquiry X; Laplace, Essai (1814)
How surprising is this claim, and is the evidence as strong as the claim is big?
Popper's line between science and non-science, not a verdict on worth. He allowed that "in practice a single conflicting or counter-instance is never sufficient methodologically for falsification".
Sources named: Thornton, "Karl Popper", Stanford Encyclopedia
What would have to happen to show this is wrong?
A statistic, a score, a prediction or a target.
Kahneman and Tversky (1974) found base rates "effectively ignored" once a description was given; Koehler (1996) concluded that base rates "are almost always used". Both are reviews of experiments, and they weigh the same studies differently.
Sources named: Tversky & Kahneman, Science (1974); Koehler (1996)
How common is this in general, before you look at the details?
"When a measure becomes a target" is Marilyn Strathern's wording (1997). Goodhart's own 1975 version was narrower: a statistical regularity "will tend to collapse once pressure is placed upon it for control purposes".
Sources named: Strathern (1997); Goodhart (1975), as quoted by Takeda and Ueda
Is this number being chased as a target? Does it still measure what it used to?
Alfred Korzybski's, from 1931 and Science and Sanity (1933). The full sentence is not a warning against maps: "if correct, it has a similar structure to the territory, which accounts for its usefulness."
Sources named: Korzybski, Science and Sanity (1933)
Where does this model or chart match the real thing, and what does it leave out?
It rests on a real tournament with published results (2014), finding "three psychological drivers of accuracy: training, teaming, and tracking"; a 2015 paper describes putting top performers into "elite teams of superforecasters".
Sources named: Mellers et al., Psychological Science (2014); Perspectives on Psychological Science (2015)
Are you keeping score of how your past forecasts turned out?
Someone did something and you are trying to make sense of it.
Robert Heinlein's 1941 story "Logic of Empire" has a close ancestor: "You have attributed conditions to villainy that simply result from stupidity." The earliest version with the name known to Quote Investigator is from 1980.
Sources named: Heinlein, "Logic of Empire" (1941); Bloch (1980)
Could this be a mistake rather than bad intent?
It began as a rule for interpreting what people mean. Quine (1960) credits the name to N. L. Wilson; his reason: "silliness, beyond a certain point, is less likely than bad translation".
Sources named: Quine, Word and Object (1960); Wilson (1959); Davidson
What is the most sensible reading of what they meant?
A measured belief "that one person's gain is possible only at the expense of other persons", tested across 37 nations (2015). A 2026 US study finds it associated with policy views (associations, not causes) and "not primarily a partisan issue".
Sources named: Różycka-Tran et al. (2015); Chinoy et al. (2026)
Does one person’s gain here really have to be the other’s loss?
Published work goes back at least to E. J. Phares in 1957; the idea became famous through Julian B. Rotter's 1966 monograph on "generalized expectancies for internal versus external control of reinforcement".
Sources named: Phares (1957); Rotter, Psychological Monographs (1966)
Do they, or you, see what happens as up to them, or as up to outside forces?
You have been at it for a while and keep going round in circles.
Aristotle's: "we do not think that we know a thing until we are acquainted with its primary conditions or first principles". For him they are starting points you grasp, not a brainstorming technique.
Sources named: Aristotle, Physics I.1
What are the starting points here that you are sure of?
The earliest printed attribution to the mathematician Carl Jacobi we found, from 1916, is hearsay: Jacobi "is said to have" taught it. Munger used inversion for avoiding failure: "I wish I knew where I was going to die, and then I'd never go there."
Sources named: Van Vleck, Bull. AMS (1916); Munger (1986)
What would make this fail for certain? Can you steer clear of that?
The famous sentence is in Zen Mind, Beginner's Mind (1970), but David Chadwick reports that a transcript of Suzuki's 1965 lecture has a plainer version, and "Only when Trudy polished it" did it take its famous form.
Sources named: Chadwick, Inquiring Mind (2008)
How would you look at this if it were your first time?
The idea is Ockham's; the famous wording is not. The Stanford Encyclopedia says the formulation "is nowhere to be found in his texts". It is a rule about needing grounds, not "the simplest explanation is usually right".
Sources named: Stanford Encyclopedia of Philosophy
Does every part of your explanation have a reason to be there?
Thinking tools, often called mental models, are short named ways of looking at a problem, such as imagining a plan has already failed or asking what happens after the first effect. This picker groups them by situation: choose yours and you see a few that might help, where each one comes from and a question to try. It is free, runs in your browser and saves nothing.
The phrase has two meanings. In psychology the idea goes back to the Scottish psychologist Kenneth Craik (1943), who proposed that the mind builds "small-scale models" of reality, and to Philip Johnson-Laird's book Mental Models (1983).
The self-help sense comes from Charlie Munger, in a talk on 14 April 1994: "You've got to hang experience on a latticework of models in your head." That is the sense used here: a set of named tools, each a different angle on a problem.
Every description in the picker comes from our Mental models cheat sheet, which follows each tool back to where it comes from and what the original says. Some well-known origin stories are more tangled than a short card can show, so each card links to the full entry with its sources.
A small team keeps missing its monthly target and wants to add a second one. Someone opens A number or a forecast and lands on Goodhart's law, whose question asks whether the number is being chased as a target and still measures what it used to. That turns the meeting from "how do we hit it" to "what was it meant to tell us".
What is a mental model?
In psychology, a small-scale model of reality the mind builds to reason with, an idea that goes back to Kenneth Craik in 1943. In self-help, a named thinking tool, the sense Charlie Munger used in a 1994 talk.
Did Charlie Munger invent mental models?
The psychology idea is older, going back to Craik (1943) and Johnson-Laird (1983). The self-help sense, a "latticework of models", is Munger's.
Which thinking tool should I use?
It depends on the situation, which is why the picker starts there. Which tools go with which situation is our own grouping, so try one and keep the ones that help.
Does the picker save anything?
No. Nothing is stored or sent; your chosen situation sits only in the page address, so a link to it can be shared.
23 tools from the Mental Models Cheat Sheet, which has more. Each description is the sheet's own wording; the full evidence, with sources, is on the page each entry links to. The situations and the questions are ours. Nothing you choose is saved or sent anywhere.
Related reading: Mental models cheat sheet · Mental Models, Checked · Mindsets, Checked · Deciding Under Uncertainty · Mental Models from Philosophy · Mental Models from History
More tools: Pre-mortem · Decision matrix · All free tools
