I used to never give up on a book but at some point, I have found a few that have drove me to that point.
Usually it's a character I just cant get in vibe with. I gave up one very popular series because I loathed the main character to the point I couldn't enjoy the series anymore.
Sometimes, though rarely, I just can't get into a book. Like I said it's rare because I am pretty good at choosing something I would like.