Save your rote copying for homework time.

So my default mode was to copy absolutely everything down (using my own personal set of abbreviations) whilst not necessarily understanding everything. Occasionally I would understand everything in the lecture; occasionally I would understand nothing in the lecture; usually it would be somewhere between the two.

Later I would copy out my notes neatly, but not allowing myself to write anything into my neat copy until I understood it. If it took me a long time to finally see how a step in a proof was justified, I would write the justification into my notes. If I had to revise something to understand the new material, I would write the relevant points I had forgotten into my notes. Hence reading my notes to revise for the exam could be as fast as possible.

To the extent that I perfectly carried out the above system, I gained near to perfect marks. To the extent that I didn't carry out the system, my marks suffered.

Sitting and thinking would only allow so much to sink in, and then I'd have none of my own notes to work off later. Instead I'd furiously transcribe by hand everything the lecturer said, everything written on the blackboard/slides (very often not the same thing) and add in my own notes on top too.

Understanding would come much later, over a much longer period than an hour-long lecture.

Not everyone can.

As someone who left numerous classes early, because confusion & anxiety over the lecture caused vomiting or diarrhea, I promise you I would have given everything to just be able to "pay attention and think."