From “Secrets of a Mind-Gamer”, a fascinating article on a normal guy who becomes a memory champion:

In his 1869 book Hereditary Genius Sir Francis Galton argued that a person could improve at mental and physical activities until he hit a wall, which “he cannot by any education or exertion overpass.” In other words, the best we can do is simply the best we can do. But Ericsson and his colleagues have found over and over again that with the right kind of effort, that’s rarely the case. They believe that Galton’s wall often has much less to do with our innate limits than with what we consider an acceptable level of performance. They’ve found that top achievers typically follow the same general pattern. They develop strategies for keeping out of the autonomous stage by doing three things: focusing on their technique, staying goal-oriented and getting immediate feedback on their performance […] To improve, we have to be constantly pushing ourselves beyond where we think our limits lie and then pay attention to how and why we fail.