Or I skip to a more interesting chapter we probably won't get to. If we had ideal teachers, we wouldn't need books. The teachers would tell us everything we need to know while being creative enough to keep our interest. They'd also give enough examples so everyone understands. Of course, they would all know massive amounts of information on every topic the course covers so that if we had any questions they could answer them.
Teachers are great, but they are still human.
There is no way they can do everything and please everyone. There was a time when we read only those books with pictures in them. Some students still can't deal with the sight of nothing but pages and pages of text. Sure, we could trim away all the fat. Our bags would be lighter.