“The concept of a coach is slippery. Coaches are not teachers, but they teach. They’re not your boss—in professional tennis, golf, and skating, the athlete hires and fires the coach—but they can be bossy. They don’t even have to be good at the sport. The famous Olympic gymnastics coach Bela Karolyi couldn’t do a split if his life depended on it. Mainly, they observe, they judge, and they guide.”