When I was younger, I would feel so badly about abandoning a book that didn't grab me, I'd force myself to slog through it until the bitter end. Then I realized that there are only so many books I'll have time to read in my lifetime so it's better to make each one count. If I'm not consistently pulled into the pages, I drop the book and crack another one. Of course there are exceptions, but it mostly means that I've enjoyed nearly all the books I've finished reading in recent years. Related, here is Goodreads' list of the most popular books users of the service have abandoned.