lots of time to think....

I sent my son off to college last week and due to his choice of colleges I now have 12 hours of thinking time when I go visit.  I spent some time thinking over character development on the way to Portland...then on the way home I started thinking about what it takes for me  not to finish reading a book. As a rule I do not post reviews of books I can't recommend, but even the ones I don't like I finish.  There was one book I disliked so much I closed it after the first chapter and returned it to the book store!  So what was it that made me close it? Poor characters?  Bad storyline? What makes you stop reading a book?