Deliberate practice is the key to expertise. This research has been replicated in many ways, and the result is consistent. The popular media dubbed this rule as a ten thousand hour rule and began to dominate the discussion about this topic. But, the 10 thousand hour rule is a half-truth. The number may vary across the domain. Maybe a chess player needs 10 thousand hours, maybe a programmer needed seven thousand hours, maybe a surgeon needs 25 thousand hours. The most important point is a “well structured, challenging, motivated, and supervised by coach” practice, a.k.a. deliberate practice.
What makes these research great? It is not grand-scale research. The main contribution of this research lies on creativity of the researchers. Using diary is not new method. But using diaries, to gain insight about how champion evolve over time is novelty.