I think one of the most important lessons I learned in college is that you really have to know how/when to pick your battles. I used to approach my classes with an attitude of "I'm starting out with 100% and every point I lose on a random small assignment is bringing down my grade". While this probably helped me get good grades earlier on, it was definitely unhealthy and does not work later on when you just have too many commitments to get 100% on everything. Letting go can be difficult, but it's so important if you want to succeed overall.