Deliberate practice is necessary, but not sufficient — at least for chess expertise:
First, not only were there several non-masters who dedicated more than 20,000 hours to chess, but there was also huge variability in the total number of hours of practice to achieve master level (Gobet & Campitelli, 2007): individual practice (min = 730 hr; max = 16,000 hr), group practice (min = 1,600 hr; max = 14,200 hr), and total practice (min = 3,000 hr; max = 23,600 hr). Second, we (Campitelli & Gobet, 2008) showed that, although titled masters and untitled international players (players with international rating but without title) did not differ in the amount of hours of practice in the first 3 years of serious dedication to chess, differences in their ratings were already apparent. This result suggests that the former benefited more from the same amount of practice than the latter.
