This from my husband the other day: "Today's thread is tomorrow's rope."
He was talking about how just when you think you can't go on any more, or you're so tired, or you're about to give up, you can actually keep going even more than you ever imagined. The thread that you're hanging on by today, turns into the rope that holds you up, the next day, when you are stronger than you thought you were.
I think back to the days of only having one baby, how little time I thought I had, and how much time I actually had. Those busy days would be like a holiday for me today, but it's only because the 'thread' has just kept on stretching out.
I guess there has to come a breaking point some time, but it may be a lot further away than I think.