People who combine their natural interests with their work are intrinsically motivated. As such they tend to put in more hours and that has a compounding effect

People who combine their natural interests with their work are intrinsically motivated. As such they tend to put in more hours and that has a compounding effect over time. Teaching oneself also has that effect. If John Carmack had a twin who wasn't so inclined and just did programming as a 9-5 career, there's no way they'd be as skilled as he is. Plus they'd probably wait until being taught how to program instead of starting to teach themselves as a kid.