"They didn't do anything, so it's not about them"

The snap at the boiler question wasn't about the boiler. You know that. Your partner didn't do anything, your daughter didn't do anything, and the sharpness in your voice belonged to someone at work who'll never hear it. Since it wasn't aimed at anyone here, the reasoning goes, nobody here should take it personally, and no real harm's done.

Laurenz Meier and Eunae Cho tested something close to this across two studies, one following 470 people over five waves and one with 131 people and their partners reporting separately. They looked at two things at work, heavy workload and rudeness from colleagues, and at what the researchers call social undermining at home, which means the small hostile things, the sharp answer, the criticism, the withdrawn warmth. Both work stressors were linked to more undermining of the partner. Two routes carried it, and they were about equal in strength. One was the bad mood itself. The other was not detaching from work in the evening. The passenger, in other words, is a route by which the day's rudeness reaches your partner, separate from the mood. Being at the desk is enough.

Arnold Bakker and colleagues studied 168 couples where both partners worked and had children. Job demands on one partner led to that partner's work getting in the way of home, which raised the other partner's load at home and their exhaustion. The route, again, was undermining. Men and women showed the same pattern. What starts as a hard day for you ends as a tired evening for someone who wasn't there.

The earlier book It wasn't about you was written for the person on the receiving end of a mood, and it argued that most moods have a day behind them that has nothing to do with the person they land on. That's true, and if your partner has read it they'll be kinder to you than you deserve. But it doesn't follow that the delivery does no harm. A parcel to the wrong address is still a parcel. The person who opens it has to deal with what's inside, and the fact that it was meant for someone else doesn't make the contents lighter. It just makes them harder to understand.

There's an honest objection, which is that you can't always control the mood. True. This book isn't going to ask you to arrive home serene. What it'll ask, in chapter 21, is that when the parcel goes to the wrong address, you say so, the same day, in plain words. The people at home can cope with a mood that's been explained. What wears them down is the unexplained one, the sharpness that seems to be about them because nothing says otherwise.