I've seen a lot of people on Goodreads and elsewhere mention that they have unbreakable compulsions that require them to finish every single book they start.
This boggles my mind. I have no problem DNFing a book I'm not enjoying. If it's not wowing me at the halfway point, the last half probably won't wow me, either. I move on until I find something I love.
How about you guys? Do you force yourself to read till "The End," even if it kills you? Or do you give up when you're feeling your eyes start to glaze over?