Done?

So many people know after their 2nd or 3rd or X child, that they are done having kids. That their family is complete at that amount. Some of my friends have even gone as far as voluntarily electing to have their tubs tied.

Which leads me this question. How do you know you are done? What is that feeling? Can you describe it?

Josh and I half-heartily (I think) joke that we are done having kids. But with every time it is said, I question if I actually mean it.