Moon-Watcher felt the first faint twinges of a new and potent emotion. It was a vague and diffuse sense of envy—of dissatisfaction with his life. He had no idea of its cause, still less of its cure; but discontent had come into his soul, and he had taken one small step toward humanity.

2001, a space odyssey: with an epilogue: After 2001 (ed. Roc, 1982)