I was on a stage once, near the end of a long conversation, and the moderator stopped me partway through a thought. Time was up. There was more, and there wasn't going to be. I said: that's life. People laughed. I meant it.

A friend of mine says it too. He says it about a man he studied under, whose working life did not go the way it should have. He tells me a little of the story, and then he stops, and says it. That's life. He isn't brushing it off. He is telling me where he put it.

That is what the phrase is for. Something was hard, or unsettling, or just sad, and you have found a way to stand next to it. Not that it was small. Not a rounding error. Only that it happened, and you have stopped arguing with it.

I have been watching water lately. In the ocean, currents curl into eddies, great slow rings of water, and sometimes a ring is pinched off from the current that made it and drifts away on its own, carrying whatever was in it. It doesn't go back. The current goes on without it. That's life.

Which is to say: that's loss. Nearly every time someone says "that's life," they mean that something was taken.

And loss is what moves people. Most of what anyone builds, the good and the bad, is an attempt to fill a hole that was left. You lose someone, and you start something. You lose a chance, and you spend years making another one.

The mathematicians I know are good at a particular thing here. They don't try to stuff something into the hole. They look at it. They find its pieces, measure the edges, see what shape it is. A coastline gets longer the closer you look at it. So does a loss. You can spend a life on the detail and never close the gap, and that is not failure. That is the work.

So when somebody stops in the middle of a sentence and says it, let them. They aren't done. They're telling you there was more, and there isn't going to be.

That's life.