Why checking seems sensible

I don't want to start by telling you the door is locked. You know it's probably locked. That was never the point, and hearing it makes you feel patronised. There are good reasons why you check, and they deserve stating before anything is said against them.

The things you check matter. A house left open, a hob left on, an email with the wrong figure to a client. These aren't trivial, and being careful about them is what a responsible adult does.

A check is cheap. Ten seconds to walk back and push a handle. Against the cost of a burglary, that's nothing. On those terms, checking is a bargain.

Memory does fail. Everyone has driven somewhere and not remembered the drive. Everyone has put something down and lost it. You know that your memory of locking the door might be wrong, because memories are.

It feels responsible. Going back is what a careful person does. Not going back, with a doubt in your chest, feels like negligence, and if something did happen you'd never forgive yourself.

It works, briefly. The moment your hand is on the locked handle, the doubt goes. That's real, and it's the reason you go back. Chapter 10 looks at how long it lasts.

And it caught something once. Years ago you went back and the door was open, or the iron was on. That memory is vivid, and it's the case for the defence every morning.

I think the habit is trying to meet four needs, and this list is mine. You want the house to be safe. You want to be a person who's careful. You want the doubt to stop. And you want to be certain, rather than merely confident, before you leave.

All four are reasonable. My argument is that the habit serves them badly. The house is exactly as safe after the first check as after the fourth. Being careful is the first check, and the rest is something else. The doubt doesn't stop with rechecking. It's fed by it. And certainty of the kind you're after isn't available from any number of looks, which is why the fourth look leaves you where the first one did, minus the clear picture you started with.