Before you start

This is a short book and you can read it in two or three sittings. It's about one habit. You and the person you live with disagree about something small, which day the plumber came, which way is quicker, what was said at Christmas, and you don't let it go. You produce the evidence. You find the calendar. You keep going until they concede, or go quiet, and you've won, and the evening has gone somewhere neither of you wanted it to.

I'm going to argue three things. The first is that the habit makes sense from the inside. You were right, often enough. Facts matter, and letting a wrong thing stand feels like a small lie. The second is that the certainty you feel is exactly what they feel, that people see bias in whoever disagrees with them and never in themselves, and that treating your partner as the biased one sets off a spiral in which each of you behaves in ways that make the other look worse. Dropping a fact isn't conceding it. Most of the facts you fight over don't matter, and the ones that do deserve a different conversation from a skirmish at dinner. The third is practical. Before you argue to be right, you ask whether it's true and whether it matters, and unless the answer to both is yes, you drop it, out loud. Chapters 19 to 22 cover how.

This book doesn't say that facts don't matter, that you should never disagree, or that you should give in on things that count. It says that being right about the plumber is a prize not worth the evening, and that there's a way to stop paying for it that isn't losing.

One caution. If disagreements in your house come with contempt, or threats, or if you're frightened of the person you live with, that isn't the habit this book is about. Arguing to be right is something people of good will do to each other. If it isn't good will, the National Domestic Abuse Helpline is free and open day and night on 0808 2000 247.

The notes at the back give my sources and their limits. Where I'm giving my own reasoning and not a finding, I'll say so.