I am an (almost independent [1] learner) mathematics student. I believe in the only way to get used to the ideas is to derive them by yourself, but when I try to derive some good and deep result, my feeling is extremely like Grothendieck here:
(...) much more "gifted" than I was. I admired the facility with which they picked up, as if at play, new ideas, juggling them as if familiar with them from the cradle—while for myself I felt clumsy, even oafish, wandering painfully up an arduous track, like a dumb ox faced with an amorphous mountain of things that I had to learn (so I was assured), things I felt incapable of understanding the essentials or following through to the end.
While rediscovering the main ideas by myself, mainly I lack clarity and depth and of thinking. Most of the time [2] feel that my thoughts are too shallow to do actual mathematics [3], much like the ox quotation. The main question is not how to have clarity and depth in thinking (although I would be happy if someone says something about those), but to how to get rid of those feelings ?
Note:
[1] By independant, I mean I do not directly interact with any other human for learning. My "school" is excessively stupid (it suppresses original thinking) and propagates "plug-n-chug" method. The other day, I asked why the Real number allows limits (or, say, partial derivatives commute)- and I ended up having an reply "It is because it is, don't ask such stupid questions" .
[2] This happens when I try to back-fill the tendrils also (as suggested by Ravi Vakil), but in a bit less degree.
[3] Suppose I want to learn (or derive the idea) of "A". I, after much struggling, do that (Occasionally I end up with a generalization or two (after given some hints)). Then, when I see the vastness and depth of generalization of "A" (by great mathematicians, usually Euler), which is ton times deeper and broad than me, I feel I am even stupid than the ox.