For a long time, I would get annoyed when I would buy a book that explained most of its main ideas in the first 10% of the book, and then just brought out example after example to hammer these same ideas into the readers head.
I realized after a while, however, that what on the surface might seem like time-wasting repetition is actually extremely useful to reinforce the concepts, and really make the reader think about them from every possible angle, and internalize them.
Humans have a cognitive bias towards thinking that if they have HEARD an idea, and don't disagree with it, that they have LEARNED that idea, but in reality, full buy-in takes a real degree of effort and time.
A book that tells you something useful is fine, but there is far greater in a value that tells you that same thing AND makes you believe and internalize it. Simply looking at the surface and judging a book using a ratio of unique concepts per page, is something I don't do anymore.