There have been plenty of books that I've started reading, but either got too into another book and forgot, or had to leave behind and forgot to pick them back up.
But there have also been some that were just so terrible I couldn't finish. Twilight for one. I think I got 13 pages in before I decided it was a stupid book about a stupid selfish girl.
Tried reading Sword of Shannara a couple times. Couldn't get into at all. It didn't grab at me. Just a bunch of boringness.
Same goes for Fellowship of the Ring. It took way to long to go anywhere. I swear I was a hundred pages in and they hadn't even left the shire. I tried, but I just couldn't push through it.
Ugh. Heinlein I am back and forth on. I read Number of the Beast even though it was a terrible horrible book. But only because I had a grade riding on it. Lets just say he has his good and bads, so choose wisely.
And I keep meaning to read Le Guin, but just haven't gotten around to it.