I suspect that Princeton (Sociology) et al. are difficult to get into, but once you are in, you are IN. And you graduate. A friend studied at Harvard; he said he took basket-weaving and easy classes the whole way through and laughed about it being easy. But hard to get into.
That was true of Yale and Harvard as well. Hard to get in, unless your family could donate a new building. But once in, it was hard to flunk out. The Ivys famously gave out what were called “Gentleman’s C” grades to anyone who actually showed up to class and turned in some sort of papers and blue books.
The fact that Al Gore, who was admitted to Harvard because his father was an influential senator, managed to get a D in Nat Sci, a famous gut course, suggests that he was beyond stupid, or maybe that he didn’t bother to turn in any work for that course.