"I can't sleep until it's sorted"

You'd say the old rule isn't a choice. You couldn't sleep anyway, lying there with it unsettled. The only route to sleep is through the settlement.

Look at what's stopping the sleep. It isn't the row being unsettled. It's the row being live. Two people at eleven, still talking, still escalating, are two people whose bodies are wide awake, and the awakeness is the argument's, and it doesn't stop because a settlement has been reached at one, because by then both of you have been at full stretch for three hours and the body doesn't stand down on command. Marie Vandekerckhove and Raymond Cluydts, in a 2010 review, described the two-way relationship. Emotional stress during the day affects sleep that night, and lost sleep makes people more sensitive to emotional and stressful events the next day. A row at one in the morning is the first half of that loop feeding the second, and the second feeding tomorrow night's row.

What lets you sleep isn't the settlement. It's the truce. A truce is a stop that both of you have agreed, with a time attached, and it does something a settlement at one can't, which is let the body stand down while the argument is still open. You know you'll be back at the table at eight. The row isn't finished but it isn't live, and a not-live row is a thing you can lie next to, cross, and sleep.

An earlier book in this series is about the mind at three in the morning, and its argument is that the night is where problems circle and don't get solved, and that a note and a time in the morning is what lets the circling stop. The same is true of a shared problem. The note says what the row is about. The time says when you'll return to it. Between the two, the thing is held, and holding is what sleep needs.

So "I can't sleep until it's sorted" is true if sorted means live, and false if sorted means held. Chapters 20 to 22 are about holding it, and most couples who try a truce with a time attached are surprised by how quickly they sleep, because what was keeping them up was never the disagreement. It was the fact that nobody had stopped.