I have made it a rule of my life never to regret and never to look back. Regret is an appalling waste of energy, and no one who intends to become a writer can afford to indulge in it. You can't get it into shape; you can't build on it; it's only good for wallowing in.
"Je ne parle pas français," from Bliss and Other Stories (1920)
Bliss & Other Stories.[digital.library.upenn.edu]