You blocked two hours to make progress on a file. Three messages, a question from a colleague and one notification later, you've produced half a page. The time was there, the attention wasn't.
What an interruption really costs
The work of Gloria Mark, a researcher at the University of California, Irvine, produced a figure that gets quoted a lot: after an interruption, it takes an average of 23 minutes and 15 seconds to come back fully to the original task.
And the return isn't direct: the brain first goes through two or three other micro-tasks before picking up the thread again, as this overview of the cost of interruptions at the office points out.
A day cut into pieces every twenty minutes contains no deep work at all, whatever its total length. You never reach any depth in it, you just restart permanently.
What deep work actually means
The term comes from Cal Newport, a computer science professor at Georgetown, in his book Deep Work, published in 2016. His definition rests on three simultaneous criteria.
The task has to be cognitively demanding, meaning it genuinely draws on your capacities. It has to unfold without interruption, which takes far more than the intention not to be disturbed. And it has to create new value rather than maintain what already exists.
That definition rules out a lot of things, deliberately. Handling your email, updating a tracker, sitting through a status meeting: useful, sometimes necessary, but not deep work. Confusing the two leads you to believe you're working deeply all day, and to wonder why nothing important is moving.
Why twenty-five minutes isn't enough
The Pomodoro technique is genuinely useful, but not on this ground.
A complex problem requires loading context: the constraints, the previous attempts, the links between the pieces. That loading takes time, and it is lost at every interruption.
On a task you can break up, a twenty-five-minute sprint works very well. On a problem that takes twenty minutes just to find where you left off, nothing is left of the sprint.
| Need | Format that fits |
|---|---|
| Getting started when you're procrastinating | Short sprints |
| Getting through repetitive tasks | Short sprints, back to back |
| Solving a complex problem | A 90 to 120-minute block |
| Writing, designing, analyzing | A long, protected block |
Building a deep work block that holds
Deciding to focus isn't enough. The block gets built, and it gets defended.
Put it in the calendar, not in your head. A slot that exists nowhere will be taken by someone else. The principle is that of time blocking: deciding in advance rather than arbitrating in the moment.
Choose the task the day before. Opening a two-hour block while wondering what to work on costs you the first twenty minutes, and the momentum with them.
Cut the source, not the notification. Closing the messaging tab works better than putting your phone on silent, because in the second case the temptation to go and look stays intact.
Plan an end. A block with no finishing time turns into a vague promise. Knowing it ends at 11:30 helps you hold it to the end.
90 minutes, not 30
Under an hour, getting up to speed eats the block. It's the first setting to fix when deep work isn't producing anything.
Two to four hours a day, no more
That order of magnitude comes up often, and it has the merit of being reachable. Take it as a landmark, not as a measured standard.
Aiming for a whole day of deep focus doesn't work, and mostly produces guilt. Two ninety-minute blocks properly held are worth more than a seven-hour ambition abandoned on Tuesday.
The rest of the day isn't lost for all that. It goes to shallow work, which exists and has to happen somewhere. Giving it an explicit slot stops it from spilling over into the deep blocks.
Try deep work tomorrow morning
Block a single ninety-minute stretch tomorrow morning, with a task chosen tonight. Close your email. Write down what you produced.
One session is usually enough to measure the gap with an ordinary morning.
If your problem is getting started rather than holding on, see how to stop procrastinating. And if your attention mostly goes into what you have to remember, lightening your mental load tackles the question upstream.
Book the slot, protect the attention.
