Yet if I want to make a serious study of something, I hit the textbooks. The internet is, in my experience, a poor replacement for a stack of well written physical textbooks.
The internet may be a big library, but in many ways it's not a very good one.
Did a master's in maths with the internet in front of me the whole time. Learned almost entirely from textbooks on my desk. The internet was useful for discussing problems and ordering books from the local library.
The secret to my success was reading the textbooks and working through them. Had perhaps twenty days of formal instruction throughout, but when I added up the hours spent it was effectively me and the books for a time equal to eight months' full-time. Couldn't have done it without simply hitting the books. Can't speak for your chums. Maybe they learned in classes or lectures or practical sessions or some such. For me, it was hitting the books.
Counter-counter point. My wife went through a graphic design degree without ever buying a textbook (many of which were required for class). She borrowed them from our local library, leveraging the inter-library loan system when needed. It saved her hundreds of $$
I can't speak for anyone else, but every textbook I used during a master's in maths was available on the screen in front of me. I used paper textbooks instead. They're simply much better for serious learning.