You can't put a chicken back into a shell.
A secret once told, you cannot untell.
You can't unscramble eggs; you can't unbake a cake.
You can't follow a path that you once didn't take.
You can't unsay the words that in anger were said,
or, after the guillotine, glue back the head.
You can't call back the bullet or unfire the gun.
Sometimes you must live with the things you have done.