Learning has to be done actively. When the prof. is giving his or her lecture, you need to actively think of what new information you're being provided with AND trying to sort it out in your head to see where it fits best with the knowledge you already have. Imagine having to maintain a filing cabinet with all your ideas. And your prof. is there handing out new documents of ideas every minute or so. It would be convenient (and somewhat passive) to just file everything you learned in that class under the top most drawer and then just pile on more stuff on it during your next class. But, that big pile of unsorted documents gets hard to find later on when you need them, say when you're studying for an exam. It's better to think of connections to previous knowledge that you already have, either filing them together or at least tagging them to be under the same topic. The more connections you make, the easier it will be to find that idea when a question about it pops up during your test.
And these connections can be made with almost anything, even those that at first don't seem to be related. One good example I could think of is that moment of realization when learning about hardness in your basic geology or mineralogy class, and how it surprisingly relates to the material composition of tableware.
| Common tableware. Photo by Daria Shevtsova from Pexels |