The U.N.’s World Happiness Report — created to curtail our unhealthy obsession with G.D.P. — is dominated every year by the Nordic countries. We head to Denmark to learn the secrets of this happiness epidemic (and to see if we should steal them).

You wouldn’t think you could win a Nobel Prize for showing that humans tend to make irrational decisions. But that’s what Richard Thaler has done. The founder of behavioral economics describes his unlikely route to success; his reputation for being lazy; and his efforts to fix the world — one nudge at a time.