Why Unfinished Tasks Wear Us Out

We shut the laptop with three things hanging, a message we half-answered, a decision we parked until someone gets back to us, and a job we started and put down again. None of it’s urgent tonight and none of it will take long tomorrow, but those tasks have a way of lingering in our mind. By the time we get in bed, all the things we didn’t do might be bouncing around in our head making us feel drained yet awake.

There's a difference between the tiredness at the end of a hard day we finished and the tiredness at the end of a tough day we didn't. Sure, a demanding day takes it out of us, but the unfinished tasks can be responsible for truly exhausting us.

What It Costs To Leave Something Open

Usually, this drag from unfinished work flies under the radar. We're not thinking about the half-answered message while we make dinner, at least not on purpose. Still, the thing keeps coming back, uninvited, which suggests something in us has been keeping it live the whole time.

Keeping thoughts like these active in the brain takes up valuable real estate. How much we can “hold” in the mind is often called working memory, and it's a small amount that varies from person to person and from day to day. An unfinished job takes up a slice of it, and it goes on taking up that slice whether we want it to or not.

This is called the Zeigarnik effect, which describes how people tend to remember tasks they were interrupted during better than tasks they finished. When researchers purposefully leave someone’s goal hanging, that person then has intruding thoughts about it intruding while they do activities completely unrelated. Unfinished isn't a note we leave ourselves for later. It's a slice of capacity we're still spending on something we're not even doing.

Why It Shows Up As Drifting Rather Than Forgetting

We never actually forget the unresolved thing, which is part of why the cost is so easy to miss. We just keep drifting toward it in fragments while we're working on other things. People who report thinking more about the unfinished task make more errors on what’s actually in front of them. That unfinished, drifting thought is partly to blame, as it drains our ability to focus.

When observed in brain scans, those wandering thoughts light up the default network and executive regions. Mind-wandering definitely isn't the brain idling. It's using some of the same systems we need for whatever we’re doing right here, right now.

We'd probably guess that a head full of loose ends makes for a day of worse work, but a 2012 study found that mind-wandering predicted extremely slow responses to questions and errors across the board. The cost shows up in a handful of moments where we're simply not present, which is why it's so hard to notice in ourselves.

Why Writing Down the Unfinished Task Helps

Most of us have likely felt the tiny-yet-mighty relief of putting something in the calendar. The work still needs to get done and arguably we've added one more thing to remember, but we feel a bit lighter afterwards.

Personal goals, and just general tasks, get completed roughly three times as often when people have a plan naming when and where they'll get it done. Having people make a specific plan for an unfinished goal strips out the intruding thoughts and the interference with unrelated work. A goal held in our mind as only an intention is a question we have to keep asking, but a goal we write down with a specific date and time attached to it is one less thing to worry about.

References

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2. McVay, J. C., & Kane, M. J. (2009). Conducting the train of thought: Working memory capacity, goal neglect, and mind wandering in an executive-control task. Journal of Experimental Psychology: Learning, Memory, and Cognition, 35(1), 196–204. https://doi.org/10.1037/a0014104

3. McVay, J. C., & Kane, M. J. (2012). Drifting from slow to "D'oh!": Working memory capacity and mind wandering predict extreme reaction times and executive control errors. Journal of Experimental Psychology: Learning, Memory, and Cognition, 38(3), 525–549. https://doi.org/10.1037/a0025896

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7. Gilbert, S. J., Bird, A., Carpenter, J. M., Fleming, S. M., Sachdeva, C., & Tsai, P. C. (2020). Optimal use of reminders: Metacognition, effort, and cognitive offloading. Journal of Experimental Psychology: General, 149(3), 501–517. https://doi.org/10.1037/xge0000652