An unfinished manuscript can haunt you like a ghost. An unpublished book can devour your brain like a hungry zombie.

This too is important: skip ahead a little, or just read the ending and find a way to live with yourself about it, but for godsakes. Give yourself permission to quit a book. If after 40 or 50 pages you are slogging thru, put it down. Do it for yourself but also because it needs to be done.