The index
Every entry, by what it does for you.
Traps happen to you. Tools you pick up. Patterns you'll notice in the world. Concepts are the vocabulary underneath.
Traps
Something your mind does to you. Biases, fallacies and effects worth noticing.
- No. 0012 Ad HominemYou question a friend’s medical claim, and the reply reminds everyone that you failed biology in high school.
- No. 0037 Anchoring BiasThe seller asks $18,000, and you spend the evening deciding how far below that number you can go.
- No. 0064 Authority BiasYou shelve your doubts about a risky purchase after noticing the recommendation comes from a famous professor.
- No. 0068 Availability HeuristicAfter watching a clip of a shark attack, you cancel a beach swim you were looking forward to.
- No. 0074 Bandwagon EffectYou join the long line at a food truck before looking at its menu.
- No. 0077 Base Rate FallacyYour screening result comes back positive, and you assume you’re almost certain to have the disease.
- No. 0100 Bias Blind SpotYour colleague’s preferred candidate looks like favoritism; your own preferred candidate just seems obviously right for the job.
- No. 0124 Bystander EffectA passenger collapses, and you scan the faces around you before taking a step.
- No. 0140 Cherry PickingThe sales deck celebrates three happy customers, while the cancellation spreadsheet stays closed on the presenter’s laptop.
- No. 0191 Confirmation BiasYou decide a job offer is right, then spend the evening reading only the reviews that make it sound good.
- No. 0196 Conjunction FallacyIn the forecast meeting, a detailed story about a recession and a market crash feels likelier than a recession alone.
- No. 0217 Correlation-Causation FallacyYour best salespeople use the new dashboard most, so you make everyone use it.
- No. 0233 Curse of KnowledgeYou write six clear steps for a new hire, then spend an hour explaining what you thought needed no explanation.
- No. 0295 Dunning-Kruger EffectYou finish your first practice exam feeling ready, then the answer key reveals mistakes you didn’t even know to check.
- No. 0310 Ego DepletionAfter a day of biting your tongue, you open the snack cupboard and feel too worn out to resist.
- No. 0326 Endowment EffectYou list your old bike for $300, then realize you wouldn’t pay that much for it yourself.
- No. 0335 Escalation of CommitmentThe pilot misses its target, and you open next quarter’s budget to find more money for the plan you pitched.
- No. 0367 False Consensus EffectYou choose a remote cabin for the group trip, sure everyone wants to escape the city.
- No. 0368 False DilemmaYour manager offers two options: approve the weekend deadline, or admit you don’t care about the customers.
- No. 0403 Framing EffectYou feel safer choosing surgery with a 90% survival rate than surgery with a 10% death rate.
- No. 0409 Fundamental Attribution ErrorA coworker misses your deadline, and you decide she’s careless before asking what else landed on her desk.
- No. 0413 Gambler’s FallacyAfter five heads in a row, you put more money on tails.
- No. 0450 Halo EffectThe candidate gives a dazzling presentation, and you give their untested management skills a higher score.
- No. 0466 Hindsight BiasThe layoffs are announced, and last month’s vague worry suddenly feels like something you knew for sure.
- No. 0476 Hot Hand FallacyAfter three winning roulette bets, you double your next stake because tonight you feel unstoppable.
- No. 0483 Illusion of ControlYou choose the lottery numbers yourself, then feel less willing to swap your ticket for one the machine picked.
- No. 0484 Illusion of Explanatory DepthYou tell your child you know how a zipper works, then run out of words after the teeth come together.
- No. 0490 Illusory Truth EffectBy the third time you see the same headline in your feed, it seems less like a rumor and more like something you know.
- No. 0494 Impact BiasYou check an unanswered job application again, certain that getting the offer would make the whole year feel different.
- No. 0587 Loss AversionYou find $20 in an old coat, then lose $20 on the train and spend the evening thinking about the loss.
- No. 0635 Motivated ReasoningYou want the apartment, so you read the glowing reviews once and reread the complaints until they sound unreasonable.
- No. 0637 Motte-and-Bailey FallacyYou challenge a proposal to track every employee, and suddenly you’re defending whether managers should know what work gets done.
- No. 0650 Naive RealismYou leave a meeting certain the facts were obvious, wondering how your colleague could possibly have missed them.
- No. 0663 Negativity BiasYou reread the one harsh comment on your presentation while the ten thank-you messages sit unopened.
- No. 0681 Not-Invented-Here SyndromeA colleague offers a tool that does the job, and your team starts planning its own version without even opening the demo.
- No. 0688 Omission BiasYou leave a dangerous machine running, relieved that any accident won’t come from a change you approved.
- No. 0697 Optimism BiasYou read that most applicants get rejected, then start planning what to wear on your first day.
- No. 0703 Outcome BiasYou drive home exhausted, arrive without a scratch, and decide you were fine to drive.
- No. 0705 Overconfidence EffectYou promise the client Friday, leave no buffer, and are surprised when one ordinary snag pushes delivery into next week.
- No. 0732 Peak-End RuleYou call the whole weekend wonderful because of one spectacular dinner and the easy ride home.
- No. 0740 Planning FallacyYou promise the report by Friday, then spend the next week fixing problems your schedule never included.
- No. 0763 Present BiasYour workout starts in ten minutes, but you sit down for one more episode.
- No. 0775 Probability NeglectYou cancel a flight after picturing a crash, without checking how likely a crash is.
- No. 0846 Representativeness HeuristicA stranger talks enthusiastically about chess, and you decide he’s a mathematician before learning what he does for a living.
- No. 0887 Scope InsensitivityThe fundraiser changes from saving 200 birds to saving 20,000, and you still reach for the same $20.
- No. 0895 Selection BiasYou read glowing reviews of a difficult course, then notice that every reviewer made it to the final lesson.
- No. 0910 Self-Serving BiasWhen your presentation wins praise, you credit your preparation; when it falls flat, you blame the room’s lousy attention.
- No. 0944 Slippery Slope FallacyYour committee rejects one late application because, by next year, nobody will respect the deadline.
- No. 0979 Status Quo BiasYou renew the same phone plan again, with a cheaper offer still open in the next tab.
- No. 0990 Straw ManYou suggest fewer weekend emails, and your manager starts defending the need to work hard.
- No. 1003 Sunk Cost FallacyYou keep pouring time into something because of everything you’ve already put in.
- No. 1008 Survivorship BiasYou scroll through traders’ success stories and start planning how to quit your job.
- No. 1027 Texas Sharpshooter FallacyAfter trying twenty cuts of a sales dashboard, you find one winning customer group and call it the campaign’s intended audience.
- No. 1085 WhataboutismYou ask why your teammate shared a client’s private file, and suddenly you’re discussing a competitor’s data breach.
Tools
A lens you choose to apply. Techniques for thinking a problem through.
- No. 0001 A/B TestingYour team prefers the new signup page, but you keep the old one live for half the visitors to see what happens.
- No. 0069 BackcastingYou put a debt-free date on the calendar, then calculate what your balance must be three months before it.
- No. 0080 BATNAThe dealer holds firm on price, and you have another car lined up across town.
- No. 0087 Bayesian UpdatingThe fraud alert looks damning, until you learn how often it flags perfectly ordinary purchases.
- No. 0125 CalibrationYou open your prediction log and find that only half the things you called 80% certain actually happened.
- No. 0141 Chesterton’s FenceYou delete an old approval step, and the next payment goes to a bank account nobody verified.
- No. 0147 Circle of CompetenceYou understand the rental property’s repairs, but the agent’s spreadsheet leaves you guessing about the investment.
- No. 0167 Commitment DeviceYou ask a friend to hold your game console until Friday, before the urge to play kicks in.
- No. 0199 Consider-the-Opposite StrategyBefore sending a furious reply, you jot down three reasons your coworker’s message might not be an insult.
- No. 0239 Decision JournalSix months after a disappointing hire, you open your original notes and discover how certain you were that it would work.
- No. 0249 Deliberate PracticeYou stop replaying the whole song and spend ten minutes on the four bars where your fingers keep stumbling.
- No. 0312 Eisenhower MatrixYou spend the morning answering messages, then realize the hiring plan due next month still hasn’t moved.
- No. 0351 Explore-Exploit Trade-OffYou order your usual lunch while a new place across the street posts a menu you haven’t tried.
- No. 0381 Fermi EstimationThe launch meeting starts in ten minutes, and you still need a defensible guess at how many support agents to book.
- No. 0382 Feynman TechniqueYou can follow every sentence of the chapter, but your explanation stalls as soon as you close the book.
- No. 0386 First Principles ThinkingYour team debates which competitor’s checkout to copy, and you ask what a customer actually needs to finish buying.
- No. 0388 Five WhysYou refill the label printer again, then notice nobody knows who is supposed to order the rolls.
- No. 0452 Hanlon’s RazorYour coworker leaves you off a meeting invite, and you’re already drafting the angry reply.
- No. 0495 Implementation IntentionsWhen you shut your laptop, you trade opening the fridge for putting on your walking shoes.
- No. 0532 InversionBefore moving day, you list everything that could leave you outside the new apartment with a packed truck and no keys.
- No. 0541 Jobs to Be DoneYou buy a meal kit the week you start a new job, though you have owned a cookbook for years.
- No. 0590 Margin of SafetyYour flight lands at noon; you book the three o’clock train and leave the one o’clock ticket alone.
- No. 0618 Minimum Viable ProductBefore building a meal-planning app, you sell five people a week of menus and make the plans by hand.
- No. 0686 Occam’s RazorThree apps stop working at once, and you start reinstalling each one before checking the shared connection.
- No. 0696 Optimal StoppingYou find a rental you can afford, but keep refreshing the listings while its application deadline gets closer.
- No. 0704 Outside View vs. Inside ViewYou budget six weeks for a renovation, then learn that the last five similar jobs on your street took four months.
- No. 0754 Pre-MortemImagine the plan has already failed, then explain why. You’ll find problems you couldn’t see while hoping it would work.
- No. 0820 Red TeamingYour launch review is all green until a separate team tries to make the plan fail.
- No. 0872 Safe-to-Fail ExperimentYou test the new scheduling rule on one volunteer team, with someone ready to restore the old schedule that afternoon.
- No. 0878 SatisficingYou find an apartment within your budget and near work, then close the other rental tabs.
- No. 0886 Scenario PlanningBefore you sign a three-year lease, you sketch what happens if your biggest customer leaves or demand doubles.
- No. 0892 Second-Order ThinkingYou waive a late fee to help one customer, then next month five more customers start paying late.
- No. 0961 Spacing EffectYou finish a two-hour study session feeling fluent, then blank on the same questions a week later.
- No. 0980 SteelmanningBefore sending your rebuttal, you rewrite your coworker’s office policy proposal in a form they could recognize and defend.
- No. 1024 Temptation BundlingYou lace up your sneakers because the next chapter of your thriller is waiting at the gym.
- No. 1026 Testing EffectYou remember the answer you struggled to produce last week; you’ve forgotten the paragraph you read three times.
- No. 1057 Two-Way vs. One-Way DoorsYour team spends three meetings debating a button label it could change back before lunch.
- No. 1079 Via NegativaYour week is packed, and canceling one standing meeting helps most, delivering more than a better calendar app could.
Patterns
How the world tends to behave. Laws and dynamics that keep showing up.
- No. 0018 Adverse SelectionYou turn down another low offer for your well-maintained car because buyers price it like one hiding an expensive fault.
- No. 0119 Brooks’s LawWith the release already two weeks late, your most experienced engineer spends Monday teaching three new hires the build process.
- No. 0153 Cobra EffectYou offer a reward for each pest killed, then discover someone is breeding pests to collect it.
- No. 0180 Compounding EffectYour savings earn $500 the first year, then $525 the next, even though you haven’t added a dollar.
- No. 0212 Conway’s LawYour company sells one product, but customers need three accounts because three departments built their parts separately.
- No. 0245 Default EffectYou silence your new phone after a week of alerts from settings you never chose.
- No. 0264 Diminishing ReturnsYou hire another pair of hands, but the same cramped kitchen sends out only a few more meals.
- No. 0318 EmergenceYou stop on a clear highway, then crawl forward, though there’s no accident, roadwork, or blocked lane ahead.
- No. 0379 Feedback LoopsYou turn up the microphone to be heard, and the speakers answer with a squeal.
- No. 0412 Gall’s LawYour team has designed the entire replacement system, but nobody has yet put one real order through it.
- No. 0437 Goodhart’s LawWhen a number becomes the goal, people find ways to move the number that don’t move the goal.
- No. 0444 GroupthinkIn the budget meeting, you leave your warning unspoken as everyone nods along with the director.
- No. 0458 Hawthorne EffectWith a researcher watching you try the new app, you read every instruction you would normally skip.
- No. 0459 Hedonic AdaptationA month after buying the car you couldn’t stop thinking about, you drive it without noticing it.
- No. 0468 Hofstadter’s LawYou add two extra weeks to a software launch, then spend both fixing a dependency nobody knew was there.
- No. 0512 Information CascadeYou approve the supplier despite a bad test result, assuming the three people who approved it before you know something you don’t.
- No. 0554 Law of Triviality (Bikeshedding)Your team approves the migration plan in five minutes, then spends half an hour arguing about the launch email’s subject line.
- No. 0574 Lindy EffectYou reach past this year’s bestseller for the book people are still recommending fifty years after it appeared.
- No. 0597 Matthew EffectThe editor requests another book from the famous author while your first manuscript still sits unread.
- No. 0630 Moral HazardYour insurance pays the whole repair bill, so you accept the first quote instead of shopping around.
- No. 0665 Network EffectsYou download a new messaging app, then leave it unopened because everyone you need to reach is still somewhere else.
- No. 0679 Normalization of DevianceThe backup alarm has been silent for weeks, but every shift has gone fine, so today’s crew leaves it broken.
- No. 0721 Pareto PrincipleYour bank statement has forty small purchases, but rent and two bills swallow most of the money.
- No. 0722 Parkinson’s LawYou have all afternoon to send a simple email, and by five you’ve rewritten it six times.
- No. 0728 Path DependenceYour team keeps using the clunky database because every report, script, and hire has been built around it.
- No. 0736 Peter PrincipleYour best salesperson gets promoted, then spends every team meeting rescuing deals instead of coaching anyone.
- No. 0769 Principal-Agent ProblemYour adviser recommends a fund, and you discover it pays them more than the cheaper option would.
- No. 0773 Prisoner’s DilemmaYou check your phone while your friend talks, then look up to find your friend scrolling while you talk.
- No. 0861 Risk CompensationYou install a new collision warning system, then start following the car ahead a little more closely.
- No. 0936 Simpson’s ParadoxYour team’s conversion rate rises on both phones and computers, but the overall rate falls.
- No. 0956 Social ProofYou walk past an empty restaurant and join the line outside the one next door.
- No. 0991 Streisand EffectYou demand that a website delete an unflattering photo, and by dinner your friends are forwarding it to each other.
- No. 1009 Swiss Cheese ModelA patient gets the wrong dose even though the order has passed through a computer check, a pharmacist, and a nurse.
- No. 1030 Theory of ConstraintsYour team doubles its assembly speed, but finished orders still pile up beside the same overloaded testing bench.
- No. 1040 Tipping PointTwo people leave your weekly game night, and the remaining friends stop coming because they expect an empty table.
- No. 1043 Tragedy of the CommonsYou stop watering your lawn, but the shared reservoir keeps falling while the sprinklers run next door.
- No. 1064 Unintended ConsequencesYou turn off phone notifications, then find yourself checking the screen every five minutes.
- No. 1090 Wisdom of CrowdsYour team’s guesses for next month’s sales range widely, but their average lands closer than anyone expected.
Concepts
The vocabulary the others are built from.
- No. 0056 Asymmetric InformationYou test-drive a used car for twenty minutes; the seller has driven it for five years.
- No. 0084 Bayes’ TheoremYour screening result comes back positive, and you start making plans as if the diagnosis is settled.
- No. 0112 Bounded RationalityYou have twenty apartment listings open, a lease to sign by Friday, and no time to inspect them all.
- No. 0193 ConfoundingYou buy the supplement used by the healthiest people at your gym, without asking what else they do.
- No. 0292 Dual-Process TheoryYou reread an email you nearly sent and realize your first reply would have made the argument worse.
- No. 0307 Effect SizeThe tutoring program boasts a statistically significant gain; you look closer and find an average improvement of one test point.
- No. 0343 Expected ValueThe repair shop offers a $180 protection plan, and you weigh that price against repairs you might never need.
- No. 0355 ExternalityYour neighbor finishes a cheap backyard bonfire, while you bring the laundry inside and close every window.
- No. 0376 Fat-Tailed DistributionsYour insurance budget survives hundreds of ordinary claims, then one warehouse fire costs more than all of them put together.
- No. 0551 Law of Large NumbersYour first ten coin flips produce eight heads, and you start wondering whether the coin is fair.
- No. 0556 Leading vs. Lagging IndicatorYour support dashboard stays green all week, but unanswered tickets are piling up before customers start canceling.
- No. 0589 Map vs. TerritoryYour phone says the path continues, but you’re standing in front of a locked gate.
- No. 0591 Marginal AnalysisThe hotel offers a room upgrade for $40, and you pause before clicking.
- No. 0599 Mean vs. MedianYour boss announces that average pay is $100,000, and nobody at your lunch table earns anything close to it.
- No. 0659 Necessary vs. Sufficient ConditionsYour application meets every published minimum, but the rejection email still arrives.
- No. 0694 Opportunity CostYou accept a Saturday overtime shift, then realize it costs you the only afternoon you could spend with your visiting sister.
- No. 0698 Option ValueYou pay a little extra for a refundable ticket because you still don’t know whether you can go.
- No. 0830 Regression to the MeanAfter your lowest sales month all year, you take a course and celebrate when the next month’s numbers bounce back.
- No. 0864 Risk vs. UncertaintyYour spreadsheet gives a new store a 12% chance of failure, though nobody can explain where the 12% came from.
- No. 1102 Zero-Sum vs. Non-Zero-SumTwo teams ask for the last $50,000 in the budget, and every dollar awarded to one comes out of the other’s share.