You're replying to a Slack message, half-listening to a call, and still have the pull request open in another tab. It feels productive. Three things are moving at once. The problem is that "moving" and "being handled well" are not the same thing — and the gap between how multitasking feels and what it actually does to your output is bigger than most people assume.
There's No Such Thing as Doing Two Things at Once
Start with the uncomfortable part: outside of a small, measurable exception, human brains cannot execute two attention-demanding tasks in parallel. What we call multitasking is almost always task switching — the brain rapidly toggling between tasks rather than running them side by side. Each toggle isn't free. Cognitive psychologists David Meyer, Joshua Rubinstein, and Jeffrey Evans described this switch as happening in two stages: first a "goal shift" (deciding to stop doing A and start doing B), then "rule activation" (loading the mental rules for B back into working memory). Both stages take time, and neither one happens instantly, no matter how minor the switch feels.
Individually, a single switch might cost a fraction of a second. The problem is volume. Across a full day of pinging between a document, a chat window, and a half-finished spreadsheet, those fractions compound. Meyer's research puts the resulting productivity loss at up to 40% — not from any single task being hard, but from the constant tax of reloading context every time attention moves.
The 2.5% Who Actually Can
Here's where it gets genuinely interesting rather than just cautionary. In 2010, psychologists Jason Watson and David Strayer at the University of Utah ran 200 people through a driving simulator paired with a demanding memory-and-math task performed simultaneously. As expected, nearly everyone's performance dropped on one or both tasks. But a small group — exactly 2.5% of participants — showed no measurable drop in either task. Watson and Strayer called them "supertaskers."
That number is worth sitting with. It means roughly 1 in 40 people can genuinely run two demanding cognitive tasks at once without a performance penalty. The other 97.5% — very likely including you — are task-switching, whether it feels that way or not. Confidence in your own multitasking ability, notably, has no correlation with whether you're actually one of the 2.5%. Most people who believe they're good at it are simply unaware of the errors they're making.
What This Actually Costs You
The cost isn't evenly distributed across every kind of work. Switching penalties grow with task complexity — toggling between two simple, familiar tasks costs little; toggling between two tasks that each require sustained reasoning costs a lot. That's exactly the profile of most knowledge work: writing, coding, analysis, design. The tasks people multitask across are usually the ones where switching is most expensive.
There's also a quieter cost that shows up over time rather than in a single session: frequent task-switching has been linked to elevated stress and reduced job satisfaction, likely because the brain never gets to fully register progress on any one thing before it's pulled elsewhere.
What To Do With This Instead
None of this means single-tasking has to be rigid or joyless. A few practical shifts make the difference between fighting your own wiring and working with it:
Batch by type, not by urgency. Group similar tasks — all your emails, all your code reviews, all your quick messages — into single blocks instead of interleaving them with deep work. The switching cost within a batch of similar tasks is far lower than switching between dissimilar ones.
Make the next task explicit before you stop. Part of the "goal shift" cost comes from re-deciding what you were doing. A one-line note — "next: fix the auth bug in login.py" — cuts that re-orientation time down substantially the next time you sit down.
Treat notifications as switch requests, not neutral pings. Every notification is an invitation to pay the switching tax, whether you act on it immediately or not. Batching notification checks to set times, rather than reacting to each one as it arrives, removes dozens of small, invisible switches from the day.
The old advice to "focus on one thing at a time" often gets dismissed as obvious, mostly because it sounds like a platitude rather than a finding. The data underneath it isn't a platitude, though — it's a fairly precise description of what your brain is and isn't built to do at the same time. For the 97.5% of us, that's worth taking seriously.
Sources
- 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. — The foundational research behind the "goal shift / rule activation" model of switching cost, and the basis for the widely cited 40% productivity estimate.
- Watson, J. M., & Strayer, D. L. (2010). Supertaskers: Profiles in extraordinary multitasking ability. Psychonomic Bulletin & Review, 17(4), 479–485. — The University of Utah driving-simulator study identifying the 2.5% of "supertaskers."
- American Psychological Association. Multitasking: Switching Costs. apa.org/topics/research/multitasking — A public-facing summary of switching-cost research, including further commentary from David Meyer.
