[W]hen I put Jorge in the library I did not yet know he was the murderer. He acted on his own, so to speak. And it must not be thought that this is an 'idealistic' position, as if I were saying that the characters have an autonomous life and the author, in a kind of trance, makes them behave as they themselves direct him. That kind of nonsense belongs in term papers. The fact is that the characters are obliged to act according to the laws of the world in which they live. In other words, the narrator is the prisoner of his own premises.
Umberto Eco, Postscript to the Name of the Rose
characters, creative-process, fictional-universe, writing