[ianai]

One awesome thing about math is it is self organizing. Many topics are composed of many smaller topics. As an anecdote, we used to say people “actually learned” (high school) algebra in calculus 1 and trigonometry in calc 2/3. In those cases it was more that to solve those problems required using algebra and trig coherently.

So to learn those 1000 pages is to, to some extent, learn a core set of techniques across many different contexts. It compresses the required mental load. For the exceptions to that rule, well, you can skim over them and know enough about them to recognize their applications later.