Daniel Kahneman begins by stating that the book is written to aid those in the imagined discussion around an office water cooler—a setting he chooses because it frequently involves gossiping about the decisions of others. He explains that it is usually far easier to evaluate the probable bases for others’ decisions than to examine our own beliefs and thinking.

Kahneman challenges the expectation that a reader knows what is happening in their mind, suggesting that most of our beliefs arrive in conscious awareness without the orderly process of the rational thought we tend to believe structures our views and choices. He likens the extensive biases that shape our intuitive judgments to diseases studied by a physician, noting that studying their existence is not a challenge to the broader health of the body and that his own study likewise does not denigrate the quality of human thought. Instead, he aims to enrich our understanding of it.

Kahneman acknowledges the large debt he owes to Amos Tversky. He briefly recalls the conversational way that his research with Tversky developed, wherein the two developed hypotheses by inventing questions and proposing intuitive answers. Kahneman and Tversky came to prominence in the 1970s through work (especially the 1974 article provided in the book’s Appendix A) that challenged the then-dominant assumptions that humans are primarily rational in decision-making, and that emotional responses tend to explain most deviations from choices that would be predicted by reason.