The only way to learn it is by doing it. Doing it carefully, and in full detail, not falling into the trap of "and I understand it from there".
This. So much this. A lot of people think there is some big difference between mastery from a physical versus intellectual level. No one who is serious about learning to play a musical instrument will only play a song up to a point and then stop, saying "... no need to go further, I already know how to play the rest." I think the way the brain consolidates high level learning into long term memory is essentially the same as for "muscle memory". This is like when you learn to drive. At first, you have to think consciously about every little detail but with practice, your unconscious mind takes those over and your conscious mind is left to operate on higher and higher level concepts. Mathematics is hard and the sooner you can offload the details to your unconscious mind the better. And the only way to do that is by practice.
I consider myself to be a smart but sometimes intellectually lazy person and had to struggle to develop the habit of working problems out rigorously and completely when learning new material. The belief that you can learn material by just reading is seductive because it feels like you're saving time and getting to the interesting topics faster. But in all likelihood, this belief is false and will be proven as false the moment your understanding is put to the test, either in a real test, or when subsequent material requires a solid understanding of older material. Sure, you may indeed be understanding it at the moment you're reading and in the flow of the material. But what makes your knowledge solid and reliable even under adverse circumstances (e.g., when you're distracted or learning a difficult new subject that builds on that knowledge) is practice and repetition. This applies not just to mathematics but to learning a new framework or programming language.
This. So much this. A lot of people think there is some big difference between mastery from a physical versus intellectual level. No one who is serious about learning to play a musical instrument will only play a song up to a point and then stop, saying "... no need to go further, I already know how to play the rest." I think the way the brain consolidates high level learning into long term memory is essentially the same as for "muscle memory". This is like when you learn to drive. At first, you have to think consciously about every little detail but with practice, your unconscious mind takes those over and your conscious mind is left to operate on higher and higher level concepts. Mathematics is hard and the sooner you can offload the details to your unconscious mind the better. And the only way to do that is by practice.
I consider myself to be a smart but sometimes intellectually lazy person and had to struggle to develop the habit of working problems out rigorously and completely when learning new material. The belief that you can learn material by just reading is seductive because it feels like you're saving time and getting to the interesting topics faster. But in all likelihood, this belief is false and will be proven as false the moment your understanding is put to the test, either in a real test, or when subsequent material requires a solid understanding of older material. Sure, you may indeed be understanding it at the moment you're reading and in the flow of the material. But what makes your knowledge solid and reliable even under adverse circumstances (e.g., when you're distracted or learning a difficult new subject that builds on that knowledge) is practice and repetition. This applies not just to mathematics but to learning a new framework or programming language.