-graduate and work 100 hour+ weeks as investment banking associates.
-join other people's startups where they work crazy hours
-work hellish hours in PhDs/med school/law school
Yes, being a founder is hard and can be absolute hell at times. But so are some of the "normal" things ambitious students already do post-graduation.
It's not like YC is saying you either do an internship with free lunches, corporate yoga classes and kombucha on tap or you dive into the trenches of being a YC founder.