He's going through it over and over and over again. To the point he doesn't have to think about it much - he just knows about what distance, which club, how to hit it, which swing, etc.

I know a guy who went to HS with Daniel Summerhays. They were on the HS golf team together. They were talking about their HS days, and he asked if Daniel wanted to go hit 18 holes with him. Daniel told him that he rarely has time to actually play a round if it isn't for a tournament - he's too busy practicing.