The mysterious and growing divide between the rich and the rest in just about every wealthy country on Earth, including the U.S., is really two mysteries wrapped in one. The first mystery is why real wage growth has sped up at the top and slowed down for everybody else. But the second, more recent, and more fascinating problem is why labor’s share of the winnings in developed economies has been in decline. It’s not just that middle-class wages are falling behind the rich. Overall wages are falling behind something else — capital.