You can be exhausted without having "worked that much." Because what wears you down isn't only what you do, but everything you have to remember, anticipate, arbitrate and carry in your head at all times. This load is invisible, and that's precisely what makes it so formidable.
Understanding how our attention works (and saturates) helps us take back control. Here is what the science says about mental load, and concrete levers to lighten it.
1. Mental load and workload: two différent things
Workload is the quantity of tasks to accomplish. Mental load is the cognitive effort their management demands: remembering, planning, anticipating, juggling priorities, letting nothing drop. You can have a reasonable workload and a crushing mental load, and vice versa.
Two people in the same rôle, with the same task list, can expérience very différent mental loads depending on the number of interruptions they face, their room for autonomy, the clarity of priorities and the means at their disposal. The feeling of being swamped with "not enough resources" isn't just an impression: it's mental load overflowing.
2. Why the brain ends up saturating
Our working memory, the mental space where we handle information "live," is surprisingly limited: it can only hold a few items at a time. The brain was never designed to keep fifty tabs open at once.
When that space is saturated, the signs appear: careless mistakes, forgetting, slowness, a feeling of "brain fog," irritability, difficulty finishing what you've started. These aren't personal failings: they are the symptoms of an overloaded cognitive system.
3. The invisible attention thieves
Several well-documented mechanisms eat away at our mental resources without our noticing:
- ●The multitasking myth: the brain doesn't do two cognitive tasks in parallel. It switches very fast from one to the other, paying a cost with each switch.
- ●The switching cost: after an interruption, it often takes several minutes to fully pick up the thread of what you were doing. Multiply that by the number of interruptions in a day.
- ●Attention residue: when you move from one task to another, part of your mind stays hooked on the previous one, you're never 100% on the new one.
- ●Hyperconnection: notifications, emails and messaging fragment attention into crumbs. You think you're "staying responsive"; in reality, you no longer do anything in depth.
4. Why the mind won't switch off in the evening
This is one of the most useful phenomena to know: the Zeigarnik effect. Our brain keeps unfinished tasks "active" in memory, like an alarm that refuses to switch off. That's why an unresolved matter keeps coming back, in the evening, at night, at the weekend, as intrusive thoughts or 4 a.m. waking.
And here's the good news: research has shown you don't need to finish the task to quiet this loop, simply writing a concrete plan (what, when, how) is enough to "reassure" the brain and free the mind. Thinking about a task keeps it alive; planning it closes it.
To recap, here are the main attention thieves and the counter-move for each:
| The attention thief | What it costs | The counter-move |
|---|---|---|
| Multitasking | The brain constantly switches and loses précision and speed. | One task at a time, in dedicated time blocks. |
| Interruptions | Several minutes to refocus after each break. | Protected slots, notifications off. |
| Attention residue | Part of the mind stays hooked on the previous task. | Close (or note) a task before moving to the next. |
| Unfinished tasks | They loop endlessly, even into sleep (Zeigarnik effect). | A concrete written plan to "close the loop." |
| Hyperconnection | Attention constantly fragmented by demands. | Genuinely disconnected moments in the day. |
5. Lightening your mental load: concrete levers
- ●Externalise, always: get everything out of your head onto a reliable support (notebook, list, tool). The brain is made for thinking, not for storing. A regular "brain dump" frees resources immediately.
- ●Work in blocks: group similar tasks, devote yourself to one thing in a defined slot, rather than flitting about. Single-tasking is a skill you can retrain.
- ●Protect interruption-free slots: turn off notifications during focus periods, signal your unavailability. One protected hour beats three fragmented ones.
- ●Set an end-of-day ritual: note the next day's priorities to close the open loops. That's what lets you truly switch off once home.
- ●Reduce the number of decisions: routines for répétitive choices spare decision fatigue, which weighs heavily on mental load.
- ●Name what's missing: mental load isn't only individual. Clarifying priorities and means with your manager reduces the exhausting work of constant arbitration.
Finally, when the mind won't switch off, sleep deteriorates and rumination sets in, it's worth talking about. A health check-up helps take stock of sleep, fatigue and the signals of chronic stress, and to act before overload turns into exhaustion.
💡 Key tips
- Multitasking doesn't exist: the brain doesn't process two cognitive tasks in parallel, it switches between them, and each switch costs time, précision and energy.
- Attention residue: when you change task, part of the mind stays "stuck" on the previous one. Finishing, or at least noting, a task before starting another genuinely frees your attention.
- The Zeigarnik effect explains why the mind won't switch off in the evening: unfinished tasks stay active in memory. The counter-move isn't to finish everything, but to write a concrete plan, that alone quiets the loop.
- The brain isn't a diary: everything you keep "in mind so as not to forget" consumes mental load continuously. Externalising it (paper, list, tool) frees resources immediately.
- An end-of-day ritual, noting tomorrow's three priorities, closes the open loops and lets the brain truly switch off once the door is shut.
Sources and références
Sweller J., Cognitive Load Theory (Cognitive Science, 1988)
Cowan N., The magical number 4 in short-term memory (Behavioral and Brain Sciences, 2001)
Mark G. et al., The cost of interrupted work: more speed and stress (CHI, 2008)
Leroy S., Why is it so hard to do my work? The challenge of attention residue (2009)
Masicampo E. J., Baumeister R. F., Consider it done! Plan-making and the Zeigarnik effect (Journal of Personality and Social Psychology, 2011)
INRS, Mental load and psychosocial risks: the essentials (2022)
