Anchoring Effect
A random wheel-of-fortune spin changes your estimate of how many African nations are in the UN. The spin was meaningless. The effect was real. Why?
19746 min read
Type
Decision-making
Choosing rationally under uncertainty or conflict.
46 entriesFilter these further →
Beginner
Ages 8+, no background needed.
Bystander Effect
If you collapse on a busy street, your chances of getting help may be worse than on a quiet one. Why does a crowd of witnesses make you less safe?
19688 min read
Dunning-Kruger Effect
The less you know, the more confident you feel. The more you know, the more you see how much you don't. Why?
19996 min read
Halo Effect
Why does being attractive make you seem smarter, or sounding confident make you seem right — even when neither is true?
19208 min read
Murphy's Law
If anything can go wrong, will it? The saying is a joke — but the engineering principle behind it is dead serious.
19497 min read
Occam's Razor
When two explanations fit the evidence equally, which should you believe? The one that assumes less.
c. 13206 min read
Parkinson's Law
Give yourself a week for a task that takes an hour, and it will take a week. Why does work expand to fill available time?
19556 min read
Sunk Cost Fallacy
You paid for a concert ticket and now feel terrible. If you hadn't paid, you'd stay home. You paid, so you go. Why does a sunk cost change anything?
19857 min read
The Monty Hall Problem
Three doors, one car. The host opens a losing door and offers you the swap. Does it make any difference whether you take it?
1975 (posed), 1990 (made famous)9 min read
The Peter Principle
Why does every organisation seem to be run by people who are bad at their jobs? Because the good ones got promoted until they weren't.
19696 min read
The Prisoner's Dilemma
Two people can each do better by betraying the other — and end up worse off than if neither of them had.
195018 min read
Amara's Law
Every major technology is overhyped on arrival and underestimated a decade later. Why does intuition fail in the same direction twice?
19776 min read
Brandolini's Law
A tweet spreads a false claim to a million people. Correcting it requires essays and citations. Why does the truth always have to work harder?
20137 min read
Buridan's Ass
A donkey stands exactly halfway between two identical bales of hay. With no reason on earth to prefer either, does it starve?
c. 1340 (the attribution; the example is far older)14 min read
Chesterton's Fence
You find a fence in the middle of a field with no obvious purpose. Remove it? Chesterton says no — and the reason reveals something about reform.
19297 min read
Cobra Effect
The British paid a bounty for dead cobras to reduce the snake population. When it ended, the population was higher than before. What went wrong?
19008 min read
Cunningham's Law
Ask a question online and wait hours. Post the wrong answer and be corrected in minutes. Why is the urge to correct stronger than the urge to help?
20106 min read
Hanlon's Razor
They didn't do it to hurt you. Probably they just didn't think. How much does it matter?
19806 min read
Hofstadter's Law
It always takes longer than you think — and that's still true even after you account for the fact that it always takes longer than you think.
19796 min read
Ringelmann Effect
Add more people to a task and each person works harder, right? Experiments show the opposite. Why does individual effort fall as the team grows?
19136 min read
Semmelweis Reflex
A doctor proved handwashing saved lives. He had the data. The medical profession ignored him for twenty years. Why does evidence trigger resistance?
18476 min read
Streisand Effect
The most reliable way to ensure millions of people see something is to try to prevent anyone from seeing it.
2003 (incident), 2005 (term coined)6 min read
The Condorcet Paradox
A majority prefers A to B, and B to C, and C to A. Every voter was honest and nobody made a mistake.
178517 min read
The Abilene Paradox
Everyone at the table agreed to a trip that not one of them wanted to take. How does a group choose what every member is against?
197417 min read
Intermediate
Curious teenagers and general adult readers.
Goodhart's Law
The moment you measure something and start rewarding the number, the number stops telling you what it used to.
1975 (Goodhart's formulation), 1997 (Strathern's phrasing)14 min read
Pygmalion Effect
Can a teacher's expectation — with no basis in fact — make a student smarter? The data say yes. The mechanism is more unsettling than the result.
19687 min read
The Paradox of Choice
Put out twenty-four kinds of jam instead of six and fewer people buy any jam at all. More options, fewer decisions.
2004 (the book); 2000 (the jam study)19 min read
The Paradox of Tolerance
A society that tolerates absolutely everything, including those working to end it, does not remain tolerant for long.
19458 min read
The Tragedy of the Commons
Every herder gains by putting one more animal on the shared field. The field is destroyed by people behaving reasonably.
196815 min read
Brooks's Law
A software project is six months late. You add more developers. Now it's eight months late. Why?
19756 min read
Conway's Law
Your software will look like your org chart. Not because you planned it, but because you couldn't plan it otherwise.
19685 min read
Matthew Effect
Two equally talented people start. One gets a small early advantage. Decades later, the gap is enormous. Where did the extra distance come from?
19688 min read
Metcalfe's Law
Double the users of a network and the value quadruples. This simple mathematics is why some networks become monopolies and others die empty.
19806 min read
The Ellsberg Paradox
You know exactly how many red balls there are, and nothing about how many are black. Does knowing more make a bet more attractive?
19617 min read
The Paradox of the Court
A student agrees to pay for his lessons the day he wins his first case. He never takes a case. His teacher sues him for the money.
c. 420 BCE (traditional); earliest surviving account 2nd century CE20 min read
The Paradox of Thrift
Every family starts saving more. The economy ends up with less saving. How can everyone doing the right thing produce the wrong outcome?
19367 min read
Advanced
Undergraduate level in the relevant field.
Braess's Paradox
Add a new road to a congested city and every journey gets slower. Close the road again and the traffic speeds up.
196819 min read
Newcomb's Problem
The boxes are already filled. Does choosing one still change what is in them?
c. 1960 (posed), 1969 (published)10 min read
The Allais Paradox
Offered the same improvement in odds twice, most people take it once and refuse it the second time. Both choices feel obviously right.
1952 (posed at the Paris colloquium), 1953 (published)22 min read
The CAP Theorem
A system spread across several machines can give you consistent answers, or always answer at all. The network makes you choose.
2000 (conjectured), 2002 (proved)23 min read
The Sleeping Beauty Problem
Woken with no memory of having been woken before, how confident should you be that the coin came up heads?
1997 (posed), 2000 (named and popularised)24 min read
The St. Petersburg Paradox
A coin-flipping game whose average winnings are infinite. How much of your own money would you actually pay to play?
1713 (posed by Nicolaus Bernoulli), 1738 (published by Daniel Bernoulli)19 min read
The Two Envelopes Problem
One envelope holds twice as much money as the other. The arithmetic says swap — then says swap back, forever.
1953 (Littlewood, crediting Schrödinger), 1989 (envelope form)19 min read
The Giffen Paradox
Some things sell more as the price goes up, and the people buying them are behaving perfectly sensibly.
1895 (Marshall's third edition); 2008 (first credible field evidence)18 min read
Expert
Graduate level or specialist readers.
Arrow's Impossibility Theorem
There is no fair way to turn what a group of people each want into what the group wants. This is not a complaint about politics. It is a theorem.
1950 (paper), 1951 (book), 1963 (corrected second edition)25 min read
The FLP Impossibility Result
A handful of computers cannot be guaranteed to agree on a single value if even one of them might be slow. Not merely hard — impossible.
198523 min read