When I was doing math, let us say for example, introductory number theory, it seems to take me a lot of time to fully understand a theorem. By understanding, I mean, both intuitively and also rigorously (know how to prove or derive). However, I really find many results (even elementary results like euclidean algorithm or things like $ax+by=\gcd(a,b)$) hard to intuitively understand. I usually will be thinking about these theorems most of the spare time, whenever I am not doing anything requires my thought...
Even if I do comprehend, it takes a long time until I fully comprehend the theorem. And sometimes I may even forgot them(maybe I didn't actually fully comprehend) I feel like I am spending tons of time more than others on number theory. I mean, many of people online claim that introductory number theory is easy. Is that I am not smart enough to do mathematics and make contribution to the world of math later on since great mathematicians must have great intuition, or is that other people are not fully comprehending the theorems and it really does take a lot of time to just figure out one theorem completely?
I am very confused. I like math, but I really want to know if I am capable of doing it and make contributions. And I wish to make the best choice for myself. I appreciate any good comments or advices!
When you say that you're experiencing some difficulties understanding intuitively some elementary things, there are a couple of possibilities:
1 - By "understanding intuitively", you actually mean the point in which you have devoted enough time and effort to certain topic that everything becomes clear and straightforward. That is what understanding something really means. Most people don't reach this stage as they stop their learning process when something "makes sense".
2 - If you regard "intuition" as an immediate understanding in the same way we know that 1+1=2, let me tell you that most mathematical concepts are not amenable to that kind of intuition. As timur said, many concepts in mathematics don't have parallel in the real world. Therefore, you can not expect the euclidean algorithm and 1+1=2 to produce the same "result" in your brain. As Von Neumann said:
That's what happens. You get used to dealing with very elaborate concepts and they become second nature to you.
Finally, if you forget something you spent a great deal of time studying it but after refreshing your knowledge, you are able to regain that understanding quickly and somewhat effortlessly, it means you actually understood it very well the first time. That's how the human brain works when it comes to nonessential things.