Book Cover
The Undoing Project: A Friendship That Changed Our Minds

★ ★ ★

TL;DR: Human mind sucks. Being aware of how it sucks and a bit of why it sucks and go a long way towards being a more effective thinker.


  • Danny grows up during the Holocaust and this shapes the rest of his life. Father dies, rest of family escapes to Israel, he is very lonely and isolated.
    • Becomes charged with identifying which military divisions people should belong to when he is just 21.
    • Defining trait: always filled with self-doubt and angst and impostor syndrome
  • Amos: quintessential Israeli, incredible person. Life of all the parties. Always the smartest person in the room. See anecdotes in snippets
    • Supreme confidence, opposite of Danny
    • Only does precisely what he wants.
  • Very weird mix: Amos works in abstract, lives in real world, Danny works in the real world and lives in the abstract
    • On their partnership: as if you put a mouse in a cage with a python and came back to find them having a good discussion
  • Halo effect: If your first impression of someone or something is positive, it creates a “halo” around that person and skews all of your other judgments and evaluations positively.
  • Randomness stereotype: people think of certain processes as “random”, and they think more “random-looking” sequences are more likely to occur. Our stereotype of randomness lacks the clusters and patterns that occur in true random sequences.
  • Availability bias: the more easily people can call some scenario to mind, the more probable they find it to be.
    • After driving by a car crash, people slow down as they think car crashes are more likely
    • Easier for a Jew living in Paris in 1939 to think of how Germans acted in 1919 than to come up with story about how they act in 1941, no matter how persuasive evidence is to the contrary.
  • Hindsight bias: once you know the outcome, you will think it was way more predictable than you found it to be before knowing the outcome.
    • i.e. after an underdog wins a sports game, you think of all the reasons why they shouldn’t have been underdogs to begin with.
  • Peak-end rule: people prefer to endure more total pain so long as the experience ends on a more pleasant note. People remember the “peak” more vividly than the average
    • Trip to Disneyland: most of it is miserable, standing in line, but you remember the fun parts of going on rides
    • Made people way more likely to come back for colonoscopies by making them longer (more total pain, ends on less pain)
  • Regret theory: opposes utility theory. People making choices make them in terms of gains and losses, not in terms of absolute levels. Seek to minimize regret. Losing $100 hurts way more than winning $100 feels good.
    • When you frame a sure thing as a loss, people prefer a gamble. When you frame it as a gain, people pick the sure thing.
  • Endowment effect: people attach extra value to things they own, simply because they happen to own it.
    • i.e. stock traders
  • Undoing: as they moved through the world, people ran simulations of the future. What if I say what I think instead of pretending to agree? What if they hit it to me and the grounder goes through my legs? What happens if I say no to his proposal instead of yes? They based their judgments and decisions in part on these imagined scenarios. And yet not all scenarios were equally easy to imagine: they were constrained, much in the way that people seemed constrained when they “undid” some strategy.
    • The Focus Rule: we have a hero or actor operating in a situation, and whenever possible we keep the situation the same and have the actor move.
      • We don’t inventa gust of wind to deflect Oswald’s bullet
    • In undoing some event, the mind tends to remove things that feel surprising or unexpected. Important: “feel” != “actual probability” :)
      • Ex: man takes different route to work and dies in car crash. Easier to have him take the same route as always than change the timing of his car on that particular day/situation
  • The conjuction fallacy: demonstrated via the “Linda problem”. People violate very very basic probability to fit their own mental images.
    • Which is more probable?
      • Linda is a bank teller.
      • Linda is a bank teller and is active in the feminist movement.
    • Everyone still said Linda was more likely to be a bank teller in the feminist movement!!


If a fresh analytical approach had led to the discover of new knowledge in baseball, was there any sphere of human activity in which it might not do the same? (L47)

[Morey]'d always been just the way he was, a person who was happier counting than felling his way through life. (L169)

"Knowledge is literally prediction," said Morey. "Knowledge is anything that increases your ability to predict the outcome. Literally everything you do you're trying to predict the right thing. Most people just do it subconsciously. (L238)

The trick wasn't just to build a better model. It was to listen both to it and to the scouts at the same time. (L312)

"[Jeremy Lin]'s incredibly athletic," said Morey. "But the reality is that every fucking person, including me, thought he was unathletic. And I can't think of any reason for it other than he was Asian." (L399)

"It was like a fish not knowing he is breathing water unless someone points it out," Morey said of people's awareness of their own mental processes. (L532)

"When someone says something, don't ask yourself if it is true. Ask what it might be true of." This was his intellectual instinct, his natural first step to the mental hoop: to take whatever someone had just said to him and try not to tear ir down but to make sense of it. (L963)

Amos's commanding officer shouted for everyone to stay put -- and leave the unconscious soldier to die. Amos ignored him and sprinted from behind the wall that served as cover for his unit, grabbed the soldier, picked him up, hauled him ten yards, tossed him on the ground, and threw himself on top of him. The shrapnel from the explosion remained in Amos for the rest of his life. The Israeli army did not bestow honors for bravery lightly. As he handed Amos his award, Moshe Dayan, who had watched the entire episode, said, "You did a very stupid and brave thing and you won't get away with it again." (L1130)

The University of Michigan psychologist Dick Nisbett, after he'd met Amos, designed a one-line intelligence test: The sooner you figure out that Amos is smarter than you are, the smarter you are. (L1130)

There was this beautiful simplicity to Amos: his likes and dislikes could be inferred directly and accurately and at all times from his actions. (L1197)

Amos liked to say that stinginess was contagious and so was generosity, and since behaving generously made you happier than behaving stingily, you should avoid stingy people and spend your time only with generous ones. (L1355)

By changing the context in which two things are compared, you submerge ceratin features and force others to the surface [...] Things are grouped together for a reason, but, once they are grouped, their grouping causes them to seem more like each other than they otherwise would. That is, the mere act of classification reinforces stereotypes. If you want to weaken some stereotype, eliminate the classification. (L1443)

[Danny] thought of himself as someone who enjoyed, more than most, changing his mind. "I get a sense of movement and discovery whenever I find a flaw in my thinking," he said. (L1630)

"Wherever there is uncertainty there has got to be judgment [...] and wherever there is judgment there is an opportunity for human fallability" (L2843)

Sentences popped out of Amos's mouth that Redelmeier knew he would forever remember: "The secret to doing good research is always to be a little underemployed. You waste years by not being able to waste hours." "It is sometimes easier to make the world a better place than to prove you have made the world a better place." (L3800)

The way to stop the captain from landing the plane in the wrong airport, Amos insisted, was to train others in the cockpit to question his judgment (L4336)