Most difficult part of plebe year: time management. Every plebe thought his/her h.s. years were crazy in terms of stuff to do. They come to realize they had no idea what "swamped" really means. There is SO much to do during Ac Year especially: classes (which are usually harder than expected), studying, pro-knowledge (rates and more), chow calls, room cleaning/inspection, watch/duty (though much easier now from a time standpoint than in my day), march-on practice, parade practice, sports practice, company officer time, meal formations and meals, "mandatory fun" (e.g., pep rallies), making/updating company boards, tailor shop fittings, laundry delivery, press shop runs, watching a sport in the yard every WE, reading required newspaper articles, uniform inspections . . . and on and on. And that doesn't even cover the stuff you WANT to do, like call/text your family and friends.
Very, very, very few manage to do everything at the excellent level they expect of themselves (and USNA expects of them). You have to choose where to put your focus (hopefully, academics and for varsity athletes, sports) while managing to do the other stuff at least adequately. For example, you have an extra hour -- do you spend it making your room look better for the next day's inspection or do you spend it studying for your chemistry quiz? The added challenge is that you will feel immediate pain for having a messy room. You may figure that you can pull it together later for chemistry. That strategy may or may not work out.
So you live and learn. And along the (sometimes miserable) way, develop invaluable skills that will last a lifetime!