what's done is done
There is no changing something; it's finished or final. For example, I forgot to include my dividend income in my tax return but what's done is done—I've already mailed the form. This expression uses done in the sense of “ended” or “settled,” a usage dating from the first half of the 1400s.
Words nearby what's done is done
what with,
what'd,
what'll,
what's,
what's cooking,
what's done is done,
what's eating you,
what's good for the country is good for general motors, and vice versa,
what's good for the goose is good for the gander,
what's in a name? that which we call a rose / by any other name would smell as sweet,
what's it to you