I suspect that there was never a time in my life that I thought I would be able to read all of the books in my collection. To some extent I could fall back on the excuse that some of them were there primarily for reference; and, the more time I spend writing, the more I find that I am using more of those books for that purpose. Nevertheless, there are some that do little more than gather dust; and I think about them more as I get older.
One result is that I have begun to provide myself with some guidelines for deciding when to say, "Enough is enough" during an unsatisfactory reading experience. Where fiction is concerned, I can generally fall back on criteria for flat-out poor writing technique. In the domain of non-fiction, however, I have to worry about whether, in the midst of bad (if not excruciatingly painful) writing, there is still the chance that I might learn something of value.
In this case I have decided to use that "value" criterion as a guideline. The issue is that any sentence or paragraph may be potentially valuable, but it is immediately devalued if it turns out that the author lacks the necessary authority (invoking a linguistic game that I unashamedly picked up from Michel Foucault). For example I recently faced a 1000-page book with considerable skepticism. However, after having read the author's Introduction, I felt that I appreciated the approach he was taking. This seemed reason enough to get over my skepticism.
Unfortunately (for the author, not for me), I found that, within 150 pages, he was basically going against the guidelines he had set for himself in that Introduction. I am trying to describe this situation carefully, because it comes close to saying that the author promised one think and delivered another. Euphemistically, this could be described as "false pretenses;" but the harsher noun "dishonesty" might be just as appropriate. Either way, I felt I had grounds for rejecting the author as a credible authority, which allowed me to free up time for reading other things with a clear conscience!