Is it normal to not understand things from undergrad?
I want to ask if other people experience similar things about not understanding many things and eventually filling in the gaps later (I mean a lot of gaps :)? Or is it a debt of a student who didn't properly go through their education?

I do very often feel the same way and asked my advisors their opinion. Here is a batch of answers fused with my commentary on the subject.

There is a big gap between getting an A and actually understanding the subject.

It is normal to not understand something in your first try. It takes few tries for some people.

Those gaps will be filled over time as you work on those subjects further.

You can't really fully understand something before teaching a course on it (verbatim from my advisors).


I personally feel like I really understand 2-3 subjects and have a passing understanding of other 4-5. Unlike your case, I did not graduate early. I personally approach this with solving textbook problems without rereading the text. It really help, at least to me, to figure out what I do or do not understand. Another method is taking more advanced courses which inevitably require, at some point, some of those gaps you are missing. That is a good time to go back and repeat, learn in context.