In the 1970s, two psychologists proved, once and for all, that humans are not rational creatures. Daniel Kahneman and Amos Tversky discovered “cognitive biases,” showing that that humans systematically make choices that defy clear logic.

But what Kahneman and Tversky acknowledged, and is all too often overlooked, is that being irrational is a good thing. We humans don’t always make decisions by carefully weighing up the facts, but we often make better decisions as a result.

To fully explore this, it’s important to define “rational,” which is an unexpectedly slippery term. Hugo Mercier, a researcher at the Institut des Sciences Cognitives-Marc Jeannerod in France and the co-author of “The Enigma of Reason,” says that he’s never fully understood quite what “rational” means.