Doing just good enough to get A for exams is just like doing good enough for your boss to give you the thumbs-up and you prepare your next promotion just like you promote to the next level of education.
Being a boss on your own is different: everything that you've got is no longer just for the grades; what you have, is what you'll get. There's no longer a syllabus to follow, you need to become a know-it-all. There's no grades to determine whether you'll progress or not, there's only survival; to stay afloat and to excel in just that. There's no past year paper or seniors to ask for tips; there's only you and your guts to thrust into a future of uncertainty.
I realize, even if you don't wanna be an entrepreneur, even if there's a greater cause you want to work for, you need that fire in you to do better in whatever you're headed for. Without that flame in you, you're always bounded; bounded by a false self-imposed limit...