I noticed that some users here are astonishingly skilled at evaluating integrals and I'm not talking about integrals you can find in Calculus II that can be solved with basic/traditional techniques (e.g., Trigonometric Substitution and Partial Fraction Decomposition), I'm talking about these kind of integrals as well as these.
So my questions are:
What are the books, sources, studies, or websites you utilized to attain such a high level of mastery in solving integrals?
How do you study new integration techniques? Do you just focus on a specific technique until you mastered it? Or do you learn new techniques by stumbling upon a specific integral that you can't evaluate using your current toolbox?
How do you know which integration technique to use on a specific integral? How do you know so many special functions and where (and when) to utilize them in an integral?
I apologize if I have so many questions, this is my first post on this website. I am just amazed to see users destroy very hard integrals like it's some sixth grade algebra problem.