I don't write fiction but when I write longer-form articles, whitepapers, and so forth I find that a good percentage of the time I end up going back and chopping out a good bit of what a former boss described as "throat clearing" at the beginning. Not always; sometimes by chance I hit on a good metaphor or story or some other lead-in that works. But at least as often it's way too much digression and backstory and setup in advance of getting to the actual topic at hand.

With respect to Anathem in particular a lot of the problem is you didn't really understand what was going on for quite a while and I found that made it a bit of an effort to keep going.