Multitasking Is a Myth: What It Does to Your Focus

You are finishing a report, one paragraph left to go. An email from your boss pops up in the corner of the screen, so you open it for a second and skim. Then you go back to the report and spend a moment hunting for where you left off and what you meant to say. That moment looks like nothing. In reality you just paid a small tax, and you pay it maybe a hundred times a day.

Most of us are convinced we can do several things at once. The brain cannot. When it feels like you are multitasking, you are really just switching quickly between tasks, and every switch costs you something. The technical name for this is task switching, and researchers have been measuring it since the start of the century.

So multitasking is not a skill you can train. It is more a description of something that never actually happens inside your head. And the least comfortable part? The people who claim to handle multitasking best tend to be the worst at it. We will come back to that.

The brain does not do two things at once. It switches.

What we call multitasking is really switching. Joshua Rubinstein, David Meyer, and Jeffrey Evans laid this out in 2001 across four experiments, where people alternated between tasks like solving arithmetic problems and sorting geometric shapes. Every time they moved from one task to another, they lost time. And the harder the task, the bigger the loss.

According to their model, each switch involves two steps. First the brain has to shift its goal, deciding that it is now doing something else. Then it has to load the rules of the new task. Both take time. Until the rules are fully loaded, you make mistakes and move slower, without necessarily noticing any of it.

Try it on yourself. You are working in a spreadsheet, you flip to a document to write one sentence, then flip back. That sentence pulls you out of the logic of the spreadsheet, and on your return you have to find which row and formula you were on. This is not laziness or carelessness. It is the time the switch itself takes, and it scales with how demanding the context was that you had to abandon.

Stephen Monsell named this in a 2003 review study: switch cost. He added an uncomfortable detail. Preparation can shrink the cost, but never erase it. Even when you know in advance that you will switch in a moment, and you have several seconds to get ready, part of the loss remains. The brain simply needs a little while to stop running in the old mode.

In the lab a single switch is a matter of tenths of a second, which sounds negligible. But across an ordinary day you switch between tasks, windows, and notifications dozens or hundreds of times, and those tiny costs add up. Picture a normal morning. You start drafting an offer for a client, Slack pings, you glance at it, you come back. Five minutes later an email, two minutes after that a colleague with a "quick question." Each interruption steals a few seconds on the way back into the text, and by evening those seconds are not seconds at all but tens of minutes, plus a scattered attention that struggles to write anything smart.

Here sits the heart of the self-deception: we confuse being busy with being productive. David Meyer, one of the authors of the 2001 study, later estimated that jumping between tasks can cost up to 40% of your productive time. That figure now circulates online as hard fact. Treat it as a rough estimate rather than a precisely measured value from the lab. The original study contains no "40 percent"; it is Meyer's later interpretation for a broad audience, popularized through the American Psychological Association.

Attention residue: part of you stays behind

On top of the direct loss of time comes something sneakier. Sophie Leroy described it in 2009 in the journal Organizational Behavior and Human Decision Processes, and called it attention residue. When you jump to a new task, a slice of your attention stays hooked on the previous one.

The effect is strongest with tasks you did not finish and have no plan for when you will return to them. A colleague interrupts you mid-analysis, you have no idea when you will get back to it, and part of your brain keeps chewing on that analysis whether you want it to or not. The more of these jumps you rack up in a day, the more fragmented your head feels by the time you shut the laptop.

The worst news for "trained multitaskers"

Now the counterintuitive part. You might expect that people who multitask constantly would get good at it through sheer practice. Eyal Ophir, Clifford Nass, and Anthony Wagner at Stanford tested exactly this in 2009, publishing in PNAS. They split people into heavy media multitaskers, the kind who run several windows, a phone, music, and work all at once, and those who rarely do. Then they ran attention and memory tests. In one, participants were told to track only the red rectangles and ignore the blue ones. The heavy multitaskers could not tear themselves away from the blue, even though it was pure clutter.

The result cut against intuition. Heavy multitaskers were worse at filtering out irrelevant information. Something unrelated to the task threw them off more easily, and they held less of the actual work in memory. In the exact thing they thought they excelled at, they lagged. Do you count yourself among the people who claim to handle multitasking better than everyone around them? That confidence tends to be a warning sign, not a diploma.

It is fair to add that later studies muddied the picture. The idea that heavy multitaskers switch more slowly did not hold up across several replications, and in one they were actually faster. What has survived is the vulnerability to distraction. Practice at multitasking does not turn you into a better juggler of tasks. It is more likely to make you easier prey for whatever new stimulus shows up.

The phone on your desk drains you, even when you never touch it

Let us push one step further. Adrian Ward, Kristen Duke, Ayelet Gneezy, and Maarten Bos studied what the mere presence of a phone does in 2017. Participants worked on memory and attention tasks with the phone either in another room, in a pocket, or face down on the desk. Nobody used it. Even so, the people who kept it within sight performed worse. The authors call this brain drain: part of your brain's capacity keeps watch over the phone even while it lies silent and face down.

The effect was strongest in the people most attached to their phones. Some caution belongs here too, because later replications are not unanimous and several found no effect at all. But the direction makes sense and the fix costs nothing. When you need to think, do not leave the phone next to the keyboard. Put it in a bag, a drawer, the next room over. The gap between "face down on the desk" and "in another room" is bigger than you would guess.

Run a small experiment. Tomorrow, for two hours of focused work, park your phone in the next room and notice how often your hand drifts to the spot where it usually sits. That reach toward an empty patch of desk is precisely the attention the phone otherwise occupies in the background, even when you are not using it at all.

When multitasking genuinely works

None of this means you can never handle two things at once. There is one condition: at least one of the activities has to be automatic and undemanding. Walking and listening to a podcast go together without friction. So does folding laundry while an audiobook plays. When one activity runs on autopilot, the brain has capacity left over for the other.

Trouble starts the moment both activities compete for the same resource. Working memory has a limited capacity, and there is something like a narrow bottleneck through which only one decision passes at a time. Writing an email while following what is being discussed in a meeting does not work. Both need language and decision-making, so they fight, and you end up doing neither properly. The nastiest trap is driving. It feels automatic, but texting behind the wheel is not multitasking. It is attention-switching in a place where a single second decides everything.

Combination of activities	Can you do both at once?	Why
Walking + listening to a podcast	Yes	Walking runs automatically, listening barely loads the mind
Folding laundry + audiobook	Usually yes	Hands run a learned motion, attention stays free
Writing an email + following a meeting	No	Both need language and decisions, sharing the same circuit
Driving + texting	No, and dangerous	Driving is less automatic than it looks

You can see the pattern. As long as one activity requires no active thinking, the brain keeps both in check. Once both need the same circuit, they collide and performance drops on both sides. And the pattern has a flip side. The moment a podcast gets interesting enough that you want to take notes on it, it stops running in the background, and walking-plus-listening suddenly fights just like email-plus-meeting.

What to do about it, in brief

The good news is that the answer is not heroic willpower but removing the switching. The foundation is called monotasking: you do one thing until you reach a natural stopping point, and only then switch. It sounds boring, and it is boring. It also works better than any trick for "better multitasking."

The second piece is batching. Instead of watching email and chat continuously, reserve two or three windows a day for them and keep them closed the rest of the time. Turn off notifications that solve nothing in real time. Most "urgent" messages will wait an hour without anything happening.

How much switching costs you also depends on how your working style is wired, whether you need quiet and one task at a time or thrive on variety and rapid changes. A work style test can help you get your bearings and show which mode brings out your best. The concrete methods for building focus and defending it from interruption are covered in our deep work guide. One rule is enough to start with. Whenever you are doing something that requires thinking, close your email. Not mute it. Close it.