I think you hit the nail on the head that one of the most important things a good teacher does is stress the important information. You can pick up a book on a

I think you hit the nail on the head that one of the most important things a good teacher does is stress the important information. You can pick up a book on anything (calculus, computer science, philosophy, etc) and just due to information-density, get lost in the minutia. A good teacher stresses the important points so you can get a broader understanding. Then you can go back for the minutia when it is needed.