Your brain can only do one thing at a time

You're deep in an important task. A message appears. A quick look, two lines read, phone back down. Ten seconds at most. To you it feels like nothing. To your brain it's a different story. Psychologist and neuroscientist Elke Geraerts explains in an interview with Het Belang van Limburg how much pressure our concentration is under. Office workers switch activities every few minutes on average, research shows. One email, WhatsApp message or colleague is enough to move attention elsewhere. After that, the brain has to find its way back to where it left off. The problem sits less in those few seconds of distraction than in what happens next.

Multitasking barely exists

We like to say we're good at multitasking. Building a presentation while Slack pings, answering email in between, quickly looking something up on the side. Except the brain does none of those things simultaneously. What we call multitasking is really switch-tasking: rapidly toggling between different cognitive jobs. Every switch demands fresh orientation. Where was I? What was I about to do? What information did I have in my head for this?

Geraerts calls this a major hidden cost of modern work. It feels active and efficient, while the switching itself consumes time and mental energy.

Experimental research on task switching shows the same principle. Psychologists Joshua Rubinstein, David Meyer and Jeffrey Evans described as early as 2001 how people have to reconfigure cognitive processes with every task change. Even very brief switches produce measurable switching costs. The frequently cited estimate: heavy switching can eat up to roughly 40 percent of productive time, depending on the complexity of the tasks.

Something different every three minutes

Researcher Gloria Mark of the University of California, Irvine has tracked for years how knowledge workers distribute their attention across a working day. Her observations of information workers show that people switch activities roughly every three minutes on average. Count only the switches between computer windows and the pace runs even higher in some studies.

An important detail: the blame rarely sits with someone else alone. An incoming message is an external interruption. We interrupt ourselves at least as easily. Opening the news for a second. A quick search. Checking whether anyone has replied yet. The brain needs no notification at all to get distracted. The mere possibility of switching is frequently enough.

That one interruption lingers

Another study shows what happens after someone gets interrupted. People turn out to be surprisingly good at compensating for lost time: they simply work faster. That speed carries a price. The researchers measured more stress, frustration, time pressure and effort in interrupted work. Which makes the idea of a quick look misleading.

The ten seconds you spend on a message are rarely the full cost. Afterwards your attention has to land again. And meanwhile the next stimulus is already waiting.

Geraerts sums it up sharply: a small interruption keeps working in your head long after the fact, and at the same time makes you more receptive to the next distraction.

Focus starts with boundaries

The solution sounds almost old-fashioned in its simplicity: create periods in which only one thing exists.

Geraerts works with clearly bounded time blocks herself. In the morning she reserves around two hours for one important task. Email off. Phone silent. Messages and conversations follow later. Then she deliberately steps away from the screen before the next focus block begins. There's an important principle behind that.

Elke Geraerts (photo: Boumediene Belbachir)

Focus arises from more than trying harder to concentrate. You make focus easier by deciding in advance what gets no access to your attention for a set period.

An hour of writing also means: an hour without email. Half an hour of studying also means: half an hour without WhatsApp. Twenty-five minutes of thinking also means: twenty-five minutes without any other task.

The boundary matters at least as much as the task itself.

Boredom has a function

More striking still is Geraerts' plea for something we try ever harder to eliminate: boredom. We fill an empty moment almost automatically. On the train, in the lift, at the coffee machine, while waiting: phone out. Yet precisely when the constant stream of stimuli stops, mental space opens up. Geraerts describes how boredom, after the initial awkwardness, makes room for new ideas and renewed focus. Perhaps we can leave some moments unoptimised. Some moments deserve to stay empty.

Protect attention before you need it

We treat concentration as if it's automatically available the moment important work begins.

The science shows something else. Attention is sensitive to environment, habits and interruptions. Whoever switches dozens of times all morning then asks that same brain to suddenly think deeply for an hour. That's a hard transition.

The alternative is making room in advance. Phone away. Notifications off. Pick one task. Mark out the time. Begin. Focus turns out to be less about willpower than about design. Protect your attention before you need it.

Sources

• Vanbaelen, S. (2026). "Een sms'je bekijken tijdens het werk? Het kost je 25 minuten", interview with Elke Geraerts, Het Belang van Limburg, 17 January 2026.
• Mark, G., Gonzalez, V. M. & Harris, J. (2005). No Task Left Behind? Examining the Nature of Fragmented Work. Proceedings of CHI 2005.
• Mark, G., Gudith, D. & Klocke, U. (2008). The Cost of Interrupted Work: More Speed and Stress. Proceedings of CHI 2008.
• Rubinstein, J. S., Meyer, D. E. & Evans, J. E. (2001). Executive Control of Cognitive Processes in Task Switching. Journal of Experimental Psychology: Human Perception and Performance, 27(4), 763–797.
• American Psychological Association. Multitasking: Switching Costs.

The starting point for this article is the interview with Elke Geraerts in Het Belang van Limburg. The scientific findings mentioned are linked to the underlying studies where possible. Figures vary per study, task and work environment.

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