Malcolm Gladwell is a horse's arse. Here's a better rule of thumb, or maybe just an observation I heard one time: You can become very good at something if you ENJOY practicing it. Then you'll put in plenty of hours and not even notice it. I certainly got good at coding because I enjoyed practicing. The person I heard the rule from was applying it to learning languages. About lot of great guitar players including Jimi Hendrix, it is said that you never saw them without a guitar in their hands.