Having your book turned into a movie is like seeing your oxen turned into bouillon cubes.
- John le Carré
The quote above is not the reason that I will include only films about literature and not literature that has been filmed. There are just too many in the second category. It seems as though every other book gets made into a movie.
But yes, how often have I said "the book was much better than the movie"... Although some are fabulous. The Lord of the Rings for example.