I'm going to be a little contrary to the consensus, but the 10,000-hour rule has merit. Of course, I'm not talking about a precise number, here, but I don't think mastery can be achieved short of thousands of hours of practice. Sure, you can learn to play and even become proficient in much less time, but greatness or mastery requires a much more significant level of commitment, whether learning bass, playing golf or practicing law or medicine.