Anders Ericsson (1947–2020) was a Swedish psychologist who spent his career studying how expert performance is acquired. His central finding is that expertise comes from a specific kind of practice rather than from accumulated experience or innate talent.

Deliberate practice

Studying violinists at the Berlin Academy of Music in 1993 with Krampe and Tesch-Römer, Ericsson found that the strongest students had accumulated substantially more hours of solitary, structured practice than their less accomplished peers.

The quality of that practice was the point. Deliberate practice has defining features: it targets a specific weakness rather than running through what you can already do, it operates just beyond current ability, it produces immediate feedback, and it requires full concentration, which limits it to a few hours a day.

This is why experience and expertise come apart. Twenty years of performing a task at a comfortable level produces very little improvement after the first few, because nothing in the routine forces a weakness into view. Most professional work has this shape.

The ten thousand hours problem

Malcolm Gladwell drew on the violin study for Outliers (2008) and popularized ten thousand hours as a threshold. Ericsson objected publicly and repeatedly: the figure was an average for one group in one domain, not a requirement, and the popularization dropped the conditions that made the practice effective. Hours of ordinary repetition do not accumulate into expertise.

Mental representations

His later account explains why practice works. Experts build detailed internal models of their domain, which let them perceive meaningful patterns where a novice sees undifferentiated detail. A chess master reads a position as a structure rather than as pieces. Practice builds the representation, and the representation is what enables the performance. See Peak.