"It's a rest"

This is the belief at the centre of the habit, so I'll take it first. You've been concentrating for an hour, or dealing with people, or carrying shopping. You sit down with the phone for five minutes and it feels like putting a weight down. You aren't working, and nobody's asking you for anything. Surely that counts as a break.

It's an understandable belief, because part of it is true. You have stopped doing the tiring thing, and stopping is the first half of a rest. There's also a kind of ease in scrolling. Nothing in it is difficult, and it asks for no effort that you can feel.

The second half of a rest is where it goes wrong. A tired mind recovers when it has less to process for a while. Think about what thirty seconds of the loop contains. There's a headline to read and react to, and a photo of someone you know, which sets off a small comparison whether you want it or not. Then there's an advert to ignore, which takes a tiny act of ignoring. After that comes a message to read and a decision about whether to answer now or later. Each item is light. But each one is something to take in, judge and respond to, and they arrive several a minute. That is the same kind of work that made you tired in the first place, done in smaller pieces. It's a bit like taking a break from reading reports by reading a different, more colourful report.

Two studies have tested this directly. In the first, two researchers at Rutgers Business School gave 414 people a set of word puzzles, a demanding task. Partway through, some of them took a short break, during which they chose items for a shopping list. Some did the break on a phone, some on a computer, and some on paper. A fourth group had no break at all. Then everyone went back to the puzzles. The people who took their break on paper or on a computer came back refreshed and did better in the second half. The people who took the same break on a phone didn't. They took longer over the second half and solved fewer puzzles than the other two break groups. On speed, they were no different from the people who'd had no break at all. On puzzles solved they landed in between, a little ahead of the no-break group and well behind the paper and computer groups.

That study was done in a lab, with an artificial break. The second was done in real offices. Researchers in the Netherlands followed 83 PhD students through their working days. An app logged every use of their phones, and once an hour they rated how tired and how bored they felt. The results ran in both directions. The more tired or bored people were, the more likely they were to pick up the phone, which is what you'd expect. But after they'd used the phone, they reported more fatigue and more boredom than before. The authors called that result surprising. It was the opposite of what theories of work breaks had predicted.

I should be straight about the limits. The second study observed people and didn't run an experiment on them, so it can't prove the phone caused the extra tiredness. The authors say as much, and they describe their results as exploratory. One of their suggested explanations is the cost of switching back and forth between two kinds of activity. The first study used one kind of break and one kind of task. Neither study settles the matter alone. But they point the same way, and it's the way your own evenings have been pointing.

There's a fair objection. "I enjoy it. When I watch something funny on the sofa at nine o'clock, I feel better afterwards, not worse." I believe you. Half an hour of things you like, chosen and sat down to, is entertainment, and entertainment is a good thing. I'd only ask you to call it that. Watching a film isn't rest either, and nobody minds, because nobody puts a film on for ninety seconds in a lift expecting to come out restored. The trouble comes from asking the phone to do a job it can't do. Chapter 12 makes room for the sofa at nine.

So it's worth being clear about what a short rest is. It's a few minutes in which less comes in. You might look out of a window, or stand in the kitchen while the kettle boils and do nothing else. You could walk to the end of the corridor and back, or shut your eyes on a train. None of those is exciting. That's the point of them, because they're the conditions under which attention comes back.

You can test this on yourself. After your next reach, as you put the phone down, ask whether you feel more rested or less than when you picked it up. Don't go by how it felt while you were scrolling. Go by how you feel once it's over.