By K. Anders Ericsson, PhD and Robert Pool, PhD

We’ve all heard it. “Practice makes perfect.” But in the real world things work somewhat differently. Indeed, it is often the case that a person will work at the same job or carry out the same leisure activity—playing the piano, for instance, or golfing—for ten or twenty years and not be much better than after one or two.

The reason is simple: When people are first introduced to a job or a leisure activity, it takes them a certain amount of practice to reach an “acceptable” level of performance—one where there are no obvious failures and no glaring areas that need improvement—and then it takes a bit more practice to reach the point where they can execute that performance relatively effortlessly. But once they have reached this level of rather effortless achievement, improvement stops or slows to a crawl. We see this, for example, in school teachers who teaching effectiveness (measured in terms of their students’ improvements in perform...