Predictably Irrational

Predictably Irrational: The Hidden Forces That Shape Our Decisions is a 2008 book by the Israeli-American behavioral economist and psychologist Dan Ariely. Its purpose is to challenge the assumption, central to classical economics, that people make their choices through rational and calculated thought. Ariely argues that our mistakes are not random but systematic: they recur in predictable ways, and therefore it is possible to learn to recognize them and, to some extent, avoid them.

The book draws on a wide range of experiments, scientific findings and anecdotes, many of them quite amusing, which the author uses to encourage readers to rethink what drives the people around them and themselves. It is organized in fifteen chapters that explore different mechanisms: the relative way we compare options, the influence of reference prices, the pull of the word "free", the difference between social norms and market norms, the role of emotion in decision making, and the difficulties of procrastination and self-control. Throughout, Ariely shows how our sense of our own worth can also shift depending on context.

Among the concepts he develops is the decoy or asymmetric dominance effect, by which a third option can change our preference between two others, and the idea that initial prices act as anchors that shape later judgments. He also examines how financial incentives can sometimes undermine motivation when they replace social bonds, and how arousal or strong feelings can lead people to act in ways they would never consider otherwise. From these analyses he proposes practical remedies, ranging from the redesign of health policies to systems that help young drivers.

The book was warmly received by the general public and helped bring behavioral economics to a broad audience beyond academia. It has been republished in a revised and expanded edition and was adapted for television in 2023 as The Irrational. Some of its experiments and conclusions have been debated within the scientific community, but its influence on the popular understanding of decision psychology has been considerable.