To me, a one semester course is 150 hours (10 hours classroom and homework and home study per week, 15 weeks). If you study on your own, without lectures or office hours, I imagine it should be harder.

I’m trying to read a good chunk of a math book (Analysis on Manifolds) while following a syllabus for it so that I know I’m covering roughly one semester of material in one semester of study hours. The most I can realistically devote right now is 30 minutes per day, most days per week. That means this is basically a one year project if I’m consistent enough to spend time on it everyday.

Some people seem to act like it’s extremely easy to teach yourself technical material, but I really don’t buy it unless you do one or more of 1) learn at a very shallow level 2) ignore keeping rest of your life in order and can sacrifice lots of time 3) work in a situation where you have a lot of resources and free time to do it (eg a technical lab at graduate school where reading the book is part of your actual research duties)

So I agree with you completely