"I just need to know"

It's ten at night and your daughter said she'd text when she got in. She hasn't. You check the phone. You check the traffic news for the M6. You check the phone again, then look at when she was last online. Your partner says she's probably just gone straight to bed, and that helps for about four minutes. Then you ask him again, in different words.

This kind of worry is a hunt for certainty. You know an accident is unlikely. What you can't stand is the not knowing. If someone could tell you for sure, even if the news were middling, you feel you could settle.

A group of researchers in Quebec, among them Michel Dugas and Robert Ladouceur, have spent years on this. They call it intolerance of uncertainty, and in their studies it separated people with severe chronic worry from other people better than anything else they measured. In one experiment with 42 volunteers, they used a gambling task to push people's tolerance for uncertainty up or down, and the group that had been made less tolerant went on to worry more. It was a small study, but it suggests the intolerance comes first and the worry follows from it.

Seen this way, a round of worry is an attempt to reach certainty by thinking. You run every possible version of events in the hope of arriving at the one that lets you say "right, it'll be fine". It can't succeed, because the future isn't available for inspection and no amount of thinking makes it so. That's why rounds don't end. The certainty they're looking for doesn't exist yet.

The same hunt drives the behaviours that go with worry. You check the phone, read about symptoms online at midnight, and refresh the parcel tracking. You ask someone "do you think it'll be all right?", though they can't know either. Each of these brings a drop of relief, and that's the trouble with them. The relief lasts minutes and teaches you to check again. Reading about symptoms is the worst of them, because every search turns up one frightening possibility you hadn't thought of. You close the laptop less certain than when you opened it.

Here's something you may have missed about yourself. You tolerate uncertainty very well in most of your life. You eat in restaurants without inspecting the kitchen, and you drive through green lights on the assumption that the other road is on red. You let a surgeon you met once put you to sleep. You have no certainty in any of these cases and you don't ask for it. So the intolerance isn't a feature of your character. It applies to a few particular subjects, usually the ones that matter most to you, where you've got into the habit of demanding a guarantee that you'd never expect anywhere else.

One objection is that wanting to know is only sensible, and that surely information is a good thing. It is, when it's available and when it would change what you do. If the scan result is ready, ring and get it. If the route has a closure, find another. But you know the difference between looking something up once and the fifth check of the phone in ten minutes. The fifth check isn't for information. There was no new information at the fourth.

I should add a caution. If checking has become a large part of your day, with long routines that you feel compelled to complete, or if fears about your health take up hours and visits to the doctor don't settle them, that goes beyond the everyday habit this book is about. It's worth telling a GP about, because there are specific treatments.

For the everyday version, the treatment that Dugas and Ladouceur's group developed includes practice at leaving small things uncertain on purpose. In a small trial of 26 patients, most of them no longer met the criteria for generalised anxiety disorder afterwards, and their tolerance for uncertainty had gone up. The treatment had several parts, so I can't tell you how much the practice alone contributed. But it's cheap to try.

Start with things that barely matter. Send an ordinary email without rereading it a third time. Order something and don't look at the tracking. Go to a restaurant you haven't looked up. Let a friend choose the film. When you want reassurance from someone, ask once, take the answer, and don't ask again that day. In each case you'll feel a small itch of not knowing, and the practice is to leave it alone and see what happens to it. It fades, generally within minutes. You're teaching yourself, on cheap material, that the itch can be left alone and nothing follows.