This question occurred to me yesterday evening when I closed a book about 200 pages (not quite half way) in and said, "I'm done." This morning, I decided I would skim ahead a little to see if what irritated me enough to stop reading the book would be swiftly rectified and the plot advanced in a non-irritating direction, but yesterday I was ready to put it down and never pick it up again. I realized, too, that what pissed me off so much this time was the same thing that had pissed me off a while back in another book that I put down and have never picked up since: a broken promise. I don't mean something trivial like "I know I promised to leave you the last piece of cheesecake, but I ate it anyway". I mean a heavy-duty promise that is part of the foundation of the story being told. In the previous case, it was a promise one MC made to himself. He did that, and I said, "You suck. You're an idiot. Why should I read about you any more? I'm done." (Of course, I didn't like the other MC anyway, so it was that much easier to walk away.) In this case, it was a promise between the two MCs, and one is trying to be noble and clever and protective by breaking it. Uh...no. Stupid and intolerable, IMO. I had no idea broken promises bugged me so much, but there does seem to be a pattern emerging, doesn't there.
So I'm curious. When a book is well-written and the genre/subject is one you generally enjoy, what makes you stop and put a book down and say, "I'm not reading you any more."? Or do you soldier through, trusting that the author will correct the issue?