In fiction, the conclusion is always at the end of the book. With non-fiction you sometimes know the conclusion by chapter 4. How would you keep going if you knew who the murderer was in chapter 4 of a mystery?
For some non-fiction, authors rely on a lot of repetition, but they don't always make it clear where the next new topic will begin. In a lecture once you get it you can check out. In a video you can skip to the next one. In a book? I don't possess the right coping mechanisms for books, and I wonder if they even exist.
I'm still learning to give myself permission to stop reading a non-fiction book halfway through when I 'get it'. I have a couple shelf-feet of books in my queue because of it. I think I expect there to be some profound observations they've saved until the end, like the little scenes after the credits in movies, and like movies, the random reinforcement keeps me coming back for more.
I've tried a bit of speed reading, skimming, and only reading the first sentence of every paragraph, but it all feels like I'm short-changing myself (and then truly short-changing myself in the process).
Maybe I should just read summaries and skip these books entirely.