For a few people, the main theme of their working lives becomes obvious in early childhood. Picasso’s first word was “piz”—a diminutive of lápiz, the Spanish for pencil. Given a chess set and the rules of the game at the age of 6, Bobby Fischer immediately taught himself how to play and soon had time for nothing else. And it is hard to imagine that the boy Mozart was often asked what he planned to do when he grew up. It is true that some discover their talent a little later. Matisse, for example, trained as a lawyer and took up painting only while convalescing after appendicitis. Still, I doubt if there was much talk of a career in jurisprudence after that.

All these, of course, were undoubted geniuses. Their gifts, once discovered, were so prodigious, so overwhelming, that they had no choice but pursue them. The rest of us aren’t like that. Instead, we have …