There is a kind of tired that arrives around four or five in the afternoon and does not match the day. You look at what actually got done, and it is not much, or not enough to explain how worn you feel. You were at your desk the whole time. You were, technically, working. And yet the feeling is less like effort spent well and more like something that leaked out through the gaps, every time you moved from one half-finished thing to the next.

MoMo hears this described often, usually filed under "I can't focus anymore." That framing turns it into a fault. The research points somewhere quieter and more specific. The cost may not be in the tasks at all. It may be in the moving between them.

The switch itself has a price

Move your attention from one task to another and you pay for the move. Not metaphorically. In the lab, people are measurably slower and more error-prone in the moments right after a switch, even on simple tasks with nothing at stake.[1][2] This is one of the most replicated findings in cognitive psychology, holding across decades of different paradigms rather than one lab's fluke.[3] The mind does not pivot cleanly. It reconfigures, and reconfiguring takes something.

Part of you stays with the last thing

Here is the part with a name. When you leave a task, especially one you did not finish, a piece of your attention stays behind. The researcher who first measured this called it attention residue: you perform worse on the next task because part of you is still running the last one.[4][5]

The residue is worst when the first thing was left open. And in an ordinary day, almost everything is left open. The email half-written when the meeting starts. The report you were three paragraphs into when the message came in. You carry each unfinished thing forward, quietly, into the next.

This is different from things MoMo has written about before. Telepressure was the hum of staying reachable, being on standby for a channel that never closes. This is not staying ready. This is the cost of actually moving back and forth. And it is different again from the tension that outlives a hard meeting, where the body stays keyed up after the stressor is over. That is the body still in the last room. This is the mind still in the last task.

It is not only lost minutes. It is how the day feels.

In real offices, not just labs, knowledge workers switch tasks very frequently, and getting back to what they were doing takes real, non-trivial time.[6][7] But the more telling finding is not about time. When people are interrupted, they tend to compensate by working faster to catch up. And that speeding-up shows up as measurably higher stress, frustration, and felt time pressure.[7][8] The work still gets done. It just costs more to do, and part of the cost is paid in how depleted you feel by evening, not only in minutes on a clock.

Even very brief breaks register. Interruptions of only a few seconds have been shown to meaningfully raise error rates on a task in progress.[10][2] It does not take a long derailment. It takes a break in the thread.

Does it really get worse by five?

This is where honesty matters. It is tempting to draw a clean line: switch all day, arrive at evening measurably worse. Each switch has a real cost, and it is reasonable to think many small costs across a day add up into the flat, worn feeling so many people describe. But that accumulation itself has not been cleanly measured, and the day is not a simple downhill slope. One workplace field study actually found focus peaking in mid-afternoon, with boredom highest in the morning.[9] Attention has a rhythm, not just a decline.

So the honest version is smaller and sturdier. Not "your focus is provably worst at five." Rather: the switching is real, its cost is real, and a day made mostly of switches asks more of you than the output shows.

It is worth saying what this is not. It is not a story about a willpower battery draining down. That "limited willpower" idea has failed to hold up in large, careful replication.[12] The switch-cost account does not need it. You are not running out of some finite reserve of grit. You are paying, over and over, a small tax on every transition.

What to do with this, which is nothing

The productivity version of this topic ends with a system: batch, block, close the tabs. Those are not bad ideas. But they locate the problem in you, again, one more thing to manage in a day already made of managing.

MoMo would offer something smaller. The tiredness at five isn't only about losing your focus, for many people, a good deal of it is what a day of being pulled between unfinished things actually costs, and that was always going to cost something. You do not have to reorganise your life around this. You might notice that the emptied-out feeling often has a source that isn't a personal failing, much of it can be the residue of everything you started and were not allowed to finish before the next thing began.

That kind of continuity, connecting a flat evening back to the shape of the day that made it, is part of what MoMo is built to hold. But that is a footnote. The essay is the residue.

References

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. PMID: 11518143.
Monsell, S. (2003). Task switching. Trends in Cognitive Sciences, 7(3), 134–140. PMID: 12639695.
Vandierendonck, A., Liefooghe, B., & Verbruggen, F. (2010). Task switching: Interplay of reconfiguration and interference control. Psychological Bulletin, 136(4), 601–626. PMID: 20565170.
Leroy, S. (2009). Why is it so hard to do my work? The challenge of attention residue when switching between work tasks. Organizational Behavior and Human Decision Processes, 109(2), 168–181.
Leroy, S., & Glomb, T. M. (2018). Tasks interrupted: How anticipating time pressure on resumption of an interrupted task causes attention residue and low performance on interrupting tasks. Organization Science, 29(3), 380–397.
Mark, G., González, V. M., & Harris, J. (2005). No task left behind? Examining the nature of fragmented work. CHI '05, 321–330.
Mark, G., Gudith, D., & Klocke, U. (2008). The cost of interrupted work: More speed and stress. CHI '08, 107–110.
Mark, G., Wang, Y., & Niiya, M. (2014). Stress and multitasking in everyday college life: An empirical study of online activity. CHI '14.
Mark, G., Iqbal, S. T., Czerwinski, M., & Johns, P. (2014). Bored Mondays and focused afternoons: The rhythm of attention and online activity in the workplace. CHI '14.
Altmann, E. M., Trafton, J. G., & Hambrick, D. Z. (2014). Momentary interruptions can derail the train of thought. Journal of Experimental Psychology: General, 143(1), 215–226. PMID: 23294345.
Hagger, M. S., et al. (2016). A multilab preregistered replication of the ego-depletion effect. Perspectives on Psychological Science, 11(4), 546–573. PMID: 27474142.