I used to force myself to finish books all the time, but now I don't worry about it. If it doesn't engage me within the first 60 or so pages (I always see the first chapter as an introduction so I don't like to consider that my test unless it's a long chapter) then I'll put it down.
I managed to read The Hobbitt and I didn't mind it. I could not get through the Lord of the Rings at all. I also never finished White Oleander.
I never read a few books in high school that I was supposed to, but that's what Cliffs Notes and movies were made for! I never Wuthering Heights was torture for me!
I make my class give the book a few chapters. I had a girl want me to read The Secret Garden and the class was begging me to stop. I told them that we had to try the first five chapters and then we would take a vote. By that time, most wanted to keep reading and by the end they all loved it and were sad that it ended!