Before you start

This is a short book and you can read it in two or three sittings. It's about one habit. Something you did or said, months or years ago, comes back into your head. You go through it again from the start. You reach the same ending you reached last time, you flinch, and an hour or a week later you go through it again.

I'm going to argue three things. The first is that the replays feel useful, and the feeling is understandable. They seem to be how you learn from the mistake, pay for it and guard against repeating it. The second is that they do none of those jobs. Whatever the mistake had to teach, you got from it early, and the four-hundredth replay adds nothing to the second. What prevents a repeat is a lesson you can state and a plan you can follow. The third is practical. Each old mistake can be gone through once, properly, on paper, with a few particular questions. After that you owe it no more of your evenings, and there's a simple way to respond when it turns up again. Chapters 12 to 14 cover that.

A few things this book isn't. It isn't a case for shrugging off what you've done. Chapter 9 is about the mistakes that still have something in them to mend, and it asks more of you than the replays ever did. It doesn't tell you that regret is foolish either. Some of the things you regret were real losses, and chapter 10 treats them as such.

Four cautions.

If you've been low for weeks, with little interest in things, poor sleep and a sense of hopelessness, the replaying may be part of depression and not a habit standing on its own. Please see a GP. In England you can also refer yourself to NHS talking therapies. Chapter 14 says more.

If what comes back is a frightening or violent event, such as an accident, an assault or a death, and it comes as flashbacks, nightmares or vivid images, that isn't the habit this book describes. The NHS lists those as the main symptoms of post-traumatic stress disorder, which has treatments of its own. Please talk to a GP.

If the thoughts are about harm you fear you may have done or might do, and you find yourself checking, confessing or repeating things in your head to cancel them out, that pattern may be obsessive compulsive disorder. It's treatable, and a GP or a talking therapies service is the place to start.

And if any of this comes with thoughts of ending your life or harming yourself, please get help today. In England that means NHS 111, an urgent GP appointment, or 999 if you're in immediate danger.

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