Translating Literature to the Screen

The axiom in movie criticism--if not in the movie business itself--is that first-rate literature almost never translates to the screen. The problem is that the novel can do one great thing that movies, despite their immense influence and universal appeal, cannot. It can go inside the heads of its characters to tell us what they are thinking. The movies can only attempt to show us the characters, though they have sometimes tried to do both by the device know as "voice over." But from Cervantes through Tolstoy through Henry James through Proust, interiority has been the great glory of the novel, and the movies cannot really compete with it.

(from "Reel Literature" by Joseph Epstein).