For you, the author, your book is all of one piece: a carefully crafted, complete, canonical answer to some important question. You weigh the worth of each chapter with the advantage of knowing what comes later, and how that bit of theory now enables action later.
Your reader, meanwhile, experiences your work as a line-at-a-time, multi-hour slog in the fog. Every so often, they find themselves wondering whether this particular path will end up taking them to where they want to be, and whether it's worth the fuss of pushing on and finding out. They’ve only seen what they’ve seen, and if they feel stuck within a stretch that feels like more work than it’s worth, they’ll simply stop. It doesn’t really matter how mind-blowingly valuable the rest of the book might be; that reader won’t get there. Similarly, if a reader passes through some part of the book without successfully picking out the value, or without knowing what to do with the insights they’ve gathered, then the reader’s experience is that the value is not there.
Craft is about what the you put into your book; reader experience is what they get out of it. And a book’s recommendability relies far more on the latter than the former.
Nonfiction design patterns can help close that gap, ensuring the reader gets out all that you've put in.