The two speeds of thinking, and the chapter that did not survive

Daniel Kahneman was a psychologist who, with his long-time partner Amos Tversky, spent decades studying how people make judgments and choices. In 2002 he received the Nobel memorial prize in economics for that work. Thinking, Fast and Slow, published in 2011, gathers it for general readers.

The book describes two modes of thought. One is fast, automatic and effortless, and it handles most of daily life. The other is slow and deliberate, and it is lazy: it often accepts what the fast mode suggests without checking. Many of our predictable errors come from that hand-off.

Along the way Kahneman covers anchoring, overconfidence, the way losses hurt more than equal gains please, and how our memory of an experience is shaped by its peak and its end more than by its length.

The lasting value is a vocabulary for your own mistakes. Once you know that a vivid example feels more common than it is, or that a project plan tends to ignore how long similar projects took, you can build small checks against those errors. The planning fallacy and loss aversion are among the best-supported ideas in the book.

The weak spot is the chapter on priming, which described studies where tiny cues, such as words about old age, supposedly changed people's behaviour. Many of these failed to replicate when the replication crisis hit psychology in the 2010s. Kahneman himself wrote publicly that he had placed too much faith in small studies. Readers should treat the priming material with doubt and the core ideas about heuristics with much more confidence.

The idea behind this caseLesson: Ask it to think step by step →

1. 1Before your next estimate of how long something will take, look up how long similar jobs took in the past.
2. 2When you feel instantly sure of an answer, ask what question your fast mind might have swapped in for the real one.
3. 3Before a big decision, imagine it has failed a year from now and write down why.