In the former situation you described, the actual textbook doesn't matter, it's all about the resources you described to help you along. In a lot of cases, tho

In the former situation you described, the actual textbook doesn't matter, it's all about the resources you described to help you along. In a lot of cases, those resources just don't exist, even at universities. That's why worked examples and problems with solutions are so invaluable. In fact, they're so valuable, I've spent half a decade compiling these kind of resources for mathematics and physics, back when I was a master's student. I literally crawled through professor course pages manually downloading pdfs.