Anders Ericsson and Robert Pool's 2016 book sets out thirty years of research on expert performance, and corrects the popular account that grew from it.

Practice, not hours

The central claim is that expert performance comes from a specific kind of training rather than from accumulated experience or innate talent. Deliberate practice has defining conditions: it targets a specific weakness, operates just beyond current ability, produces immediate feedback, requires full concentration, and is usually guided by someone who can see what you cannot.

This explains a common observation. Twenty years in a job produces far less improvement than twenty years might suggest, because ordinary work is performed at a comfortable level where nothing exposes a weakness. Experience accumulates and skill plateaus.

Correcting ten thousand hours

Ericsson uses the book to object to the rule drawn from his 1993 violin study. The number was an average for one group in one domain, not a threshold, and the popular version dropped the conditions that make practice effective. Hours of repetition do not accumulate into expertise; hours of deliberate practice do, and most people cannot sustain more than a few a day.

Mental representations

The explanatory core is that experts build detailed internal models of their domain. A chess master perceives a position as a meaningful structure where a novice sees individual pieces. These representations are what allow experts to plan further ahead and notice what matters, and building them is what practice actually does.

This reframes talent. Ericsson argues that measured differences in most fields reflect differences in training history rather than fixed capacity, though he accepts physical constraints such as height. See Mindset for the complementary argument about beliefs, and career capital for the compounding form.