This seems like a vague question, but please bear with me before voting to close it:
Often times, when searching for a good textbook on a particular subject (mostly mathematics or physics), I see users who confidently suggest multiple textbooks on this same subject. (Here is a good example.) My guess is that these users have not actually read through each of these textbooks page by page.
I'm currently going through a few textbooks to learn and/or brush up on different subjects. I am reading them carefully, doing the exercises, taking notes on things I don't understand, etc. A chatper, at best, takes me a couple of weeks (and I spend the majority of my free time studying).
This being said, how does a person read these text-books in-depth enough to have a founded opinion on their contents? Is it done after already knowing the material?
(I know this is a strange, perhaps difficult to answer question, and I'd be glad to take any suggestions or criticisms to better it).