The phrase 'Don't Cry over Spilt Milk' means there's no use in worrying over past events which cannot be changed.
Example of Use: "I know you didn't mean to break my phone, so there's no use in crying over spilt milk now."
While the exact origin of the idiom 'don’t cry over spilt milk' isn’t exactly known, it is quite likely to have come from faery lore. In the days when people believed strongly in fairies, it was common to lay out a shrine for them, consisting of small quantities of food and drink; particularly of their favorite drink, milk. Whenever milk was spilled, it was considered to be nothing more than a little extra offering to the fairies, and nothing to worry about.