Natural-born ability is taking a hit these days, and A-Rod is only partly to blame. In his bestselling Outliers, Malcolm Gladwell argues that success stems more from opportunity and upbringing than from innate gifts. Now, contributing editor Coyle suggests that super-achievement boils down to something called myelin, the fatty white stuff wrapping the brain's nerve circuits. And here's the good part: We can actually grow more of this neural insulator by training harder and smarter. Coyle lays out the myelin theory through visits with top neuroscientists and travels to the world's most rarefied breeding grounds—the soccer fields, music schools, and tennis courts that consistently churn out superstars. "They have entered a zone of accelerated learning that, while it can't quite be bottled, can be accessed by those who know how," Coyle writes. Athletes at Moscow's Spartak Tennis Club swing a racket for hours, no ball in sight, while a weathered coach barks orders: slow down, fine-tune, repeat. At a music school in upstate New York, violin students screech through individual measures, out of order and off rhythm. As Coyle explains it, this sort of "deep practice" not only pushes us just past the limits of our abilities but also tells our brains to produce myelin. It's an intriguing explanation for the old "practice makes perfect" idea, and Coyle presents it in a way that's always entertaining and often inspiring. And if the theory is correct, we have no one to blame but our lazy selves if we're not tearing up the courts at Wimbledon.