"Never go to bed on an argument"

Start with the old rule itself, because it's the belief the whole night rests on, and it's worth asking what it's assuming.

It assumes that a settlement is available. That if the two of you keep at it, you'll get there. And it assumes that the getting there is as possible at midnight as at any other hour, so that the only variable is persistence. Both assumptions are wrong, and the second one is measurable.

Scott Golder and Michael Macy, in 2011, analysed millions of public messages posted through the day by people in dozens of countries, and traced how the emotional tone of the messages moved with the clock. They found the same pattern everywhere. People wake in a good mood, and the mood deteriorates as the day goes on, with a small lift in the evening and then a decline toward the night. The pattern held across cultures and was consistent, the researchers said, with the effects of sleep and the body clock. It's social media data, which has limits, and it's about mood in general rather than arguments. But the shape is the thing. The late hour is the low point of the waking day for most people, most days, and the low point is where the old rule sends you to do the hardest thing a couple does.

Now add what chapter 6 will say about sleep loss and reactivity, and what chapter 11 will say about the circuit, and the old rule looks different. It isn't advice to persist. It's advice to hold the most delicate conversation of the week at the one hour when both of you are least able to hold it, and to keep holding it as that ability drains further, and to treat the draining as a reason to keep going.

Where did it come from? I don't know, and I'd guess it came from a time when a row left overnight really might be left for a month, because people didn't talk about feelings much and the night was the only time the talking happened. That's not your house. You'll be at the kitchen table at eight, and chapter 21 is about making sure you are, and once that's true the old rule has lost the one thing that justified it, which is that tonight is the only chance.

Never go to bed on an argument was said by people who meant never leave things unmended. That part is right. What they got wrong is the hour.