Just a few decades ago, more than 90 percent of 30-year-olds earned more than their parents had earned at the same age. Now it's only about 50 percent. What happened -- and what can be done about it?

Starting in the late 1960s, the Israeli psychologists Amos Tversky and Danny Kahneman began to redefine how the human mind actually works. Michael Lewis's new book The Undoing Project explains how the movement they started -- now known as behavioral economics -- has had such a profound effect on academia, governments, and society at large.