I promise you that explaining a technical advanced math subject is less obvious than this, and that even students that come in with the same background will str

I promise you that explaining a technical advanced math subject is less obvious than this, and that even students that come in with the same background will strongly disagree over which books are easiest to read. Maybe it's obvious that sketching only a little formalism is the best. But then some of your statements end up vague, and students stumble on practice problems where they really need to understand the details of the formalism. Maybe it's obvious that stating things as simply as possible is the best, even at the cost of generality. But then your statements won't be powerful enough when people try to go beyond the few simple examples you give, and people will feel betrayed. Maybe it's obvious that a historical approach is the best, for motivation. But historical papers are extremely confusing to read. They're full of redundant checks of things we know are obviously true today, and archaic notation and jargon. People will get annoyed at slogging through ten pages of text to confirm something that is obvious in a modern formalism. Maybe it's obvious that a modern, clean formulation is best. But then the definitions are unmotivated, seem to come out of nowhere, there's not enough connection to the historical development, and your book won't be compatible with older books. Maybe it's obvious that no formalism at all is best; you just show how to solve problems concretely. But this turns what could have been a few simple principles into an enormous bag of ad hoc tricks people need to memorize. Textbooks that do this are derisively referred to as "cookbooks". It is not obvious how to write a book.