覆水盆に返らず (ふくすいぼんにかえらず): what's done is done; it is no use crying over spilt milk; spilt water won't go back into its tray

what's done is done; it is no use crying over spilt milk; spilt water won't go back into its tray

For something irreversible, especially a relationship or a decision that cannot be unmade. Heavier than ordinary regret.

The same saying in Chinese: 覆水难收