Your time gravitates naturally towards what you love to do. If what you love to do intersects with your work, then it is likely that often when you are not working you are doing things that further your excellence at your trade anyway. If these extra hours are the same as the hours you work, every year you do something gives you almost 2 years of experience. And if you work hard to be 30% more efficient, that multiplies the 2x. This consistent advantage compounds over time.