In the first ever actual test of Ericsson’s initial claim, Brooke Macnamara, David Hambrick, and Frederick Oswald recently reviewed a large number of studies conducted since that 1993 paper. They found that sheer amount of deliberate practice does not, in fact, explain most of the differences in expert performance. Additionally, there were huge differences between fields, with effects for education and professions much smaller than for games, music and sports.