(yeah, this will make you feel stupid. The more you can face this feeling, the more math you'll know.)
This is probably true not only for math. It suggests a general principle of rationality: seek out situations in which you might be made to feel stupid.
This is much easier said that done. Unpleasant feelings are unpleasant, it burns will power.
I think positive conditioning on this is vital. However if this conditioning can be generalized or if it remains field specific is another question.
Learning math is hard. Those that have braved some of its depths, what did you discover that allowed you to go deeper?
This is a place to share insights, methods, and tips for learning mathematics effectively, as well as resources that contain this information.