“The writer's characters must stand before us with a wonderful clarity, such continuous clarity that nothing they do strikes us as improbable behavior for just that character, even when the character's action is, as sometimes happens, something that came as a surprise to the writer himself. We must understand, and the writer before us must understand, more than we know about the character; otherwise neither the writer nor the reader after him could feel confident of the character's behavior when the character acts freely.”