From watching another player in their group hit a shot before them. Checking the wind, knowing what club another player hit, getting a read on green from someone in your group putting on a similar line, etc.

Then on top of that, these guys play in groups all season only to have the biggest tournament of their life be 18 holes of them playing as a single. Not talking to anyone for 18 holes besides your coach or assistant coach (whenever they aren’t with the other 4 guys) gives you a lot of time to overthink things between shots.