"Along the way, Marcus explores the basic elements of music and how it evolved culturally and biologically. He dives deep into the popular "ten thousand hours" theory of mastery, developed by cognitive psychologist Anders Ericsson, "the world's leading expert on expertise," and examines Ericsson's second, lesser-known prerequisite for expertise - the notion of "deliberate practice," which describes the constant sense of self-evaluation and a consistent focus on one's weaknesses rather than playing on one's strengths. In fact, the practice of targeting specific weaknesses is known as the "zone of proximal development" and offers a framework for everything from education to videogames:
[The "zone of proximal development" is] the idea that learning works best when the student tackles something that is just beyond his or her current reach, neither too hard nor too easy. "