“What’s done cannot be undone.”
Some consequences cannot be reversed, so the practical question becomes how to respond now rather than how to erase the past.
Source details
Macbeth, Act V, Scene I, reviewed against the scan-backed 1918 Yale text. Lady Macbeth says 'What's done cannot be undone' during the sleepwalking scene; the dramatic context is guilt and psychological disintegration, not generic advice that consequences should simply be accepted.