Aside from discovering how many hours of practice it takes to achieve true mastery in a field of endeavor, what other striking thing did Ericsson's study uncover?

Opportunity, legacy, persistence, and luck are other factors.

The striking thing about Ericsson's study is that he and his colleagues couldn't find any "naturals," musicians who floated effortlessly to the top while practicing a fraction of the time their peers did. Nor could they find any "grinds," people who worked harder than everyone else, yet just didn't have what it takes to break the top ranks.