That train has left the station.

Train leaving station

Have you ever asked to add something to a project that's already finished? You might have heard, "I'm sorry, but that train has left the station." That means you can't change it now because it's been finalized.

Most of the time, this phrase is used in informal conversation.

Here are some examples:

A: She wants to change the date for the office party.
B: Are you kidding me? Everything's set for June 12! That train has left the station.

A: Do you think we'll get any more money for the project?
B: I'm afraid that train has left the station.

You can also add an adverb for emphasis:

A: I'd like to comment on the question about what color to paint the office.
B: Sorry, that train has already left the station, my friend. We decided on the light green.

A: Can I still make a change to our proposal?
B: Hurry up—that train is about to leave the station!

It's easy to see how this idiom arose. If something is already finished, then you can't change it. If a train has already left the station, then you can't get on it. It's as simple as that.