^Brown has an open curriculum, the option to take classes pass fail, a prolonged shopping period and no plus/minuses.
Yes you can fail but you have the option to drop and retake, classes are rigorous, taking all classes pass/fail will adversely impact graduate school opprtunities, and the lack of +/- can arguably inflate or deflate your implied GPA. Students typically (and I hate to generalize) are extremely collaborative and non competitive with one another, while being extremely prideful in challenging themselves as individuals and pursuing demanding areas of study. Given how competitive it is to gain admissions the typical Brown student pushes themselves extremely hard. They tend to choose Brown to avoid a cut throat atmosphere that will allow and encourage their academic curiosity while fostering friendships and a team approach.
Additionally it should be noted that this approach encourages students to explore a variety of academic subjects and ensures that all participants in a class are there based on academic curiosity not obligation. No one is taking Rock for Jocks to fulfill their science class, etc…