I definitely used to be firmly in the "if I start it, I'm finishing it" camp, but as I've gotten older and stingier with my time I've relented a little...having an actual TBR helps too because I can look at all the stuff I'd rather be reading XD I like to feel I've at least given the book a solid chance though, and if I'm at 50% still waiting for it to get good...girl it is not happening.