I am convinced that much of the gap between the best college students and the worst is explained by study habits. Frankly, most students study poorly. To make matters worse, most teachers are incapable of teaching good study habits.
Learning is proportional with effort
Sitting in a classroom listening to a professor feels like learning… Reading a book on a new topic feels like learning… but because they are overwhelming passive activities, they are inefficient. It is even worse than inefficient, it is counterproductive because it gives you the false impression that you know the material. You can sit through lecture after lecture on quantum mechanics. At some point you will become familiar with the topics and the terminology. Alas you are fooling yourself which is worse than not learning anything.