Every day you go to class, you pay attention, you read the notes, read the text, and build up a knowledge of the course material. You spend all semester working hard at understanding these concepts, maybe problems, maybe projects (whatever). Then you (mis)predict what will be on the final examination and study, you study what you think you will be asked (you can't possibly study it all - it took you almost the whole semester). You raise up these little points of information to a very high degree, but at a cost.

By remembering specific points of the course, the highlights overshadow the baseline. You push down your general knowledge of the course in order to do well on your exam.

Luckily, a few weeks after the exam, you've forgotten all the specifics of what you studied, and so some of the baseline knowledge in the course returns. Of course, as soon as you stop remembering, you start forgetting.