This Is Exactly Why You Can't Remember If You Locked the Door Behind You

There's a psychological reason why you often forget if you've finished a task, a new study shows.

We've all been there before: You're running an errand and you wonder if you forgot to lock the door or switch off the lights. Though you recall reminding yourself to do it, you can't remember if you actually did. (Cue a minor panic attack.) Well, it turns out there's a psychological reason behind this common confusion. A new study published in the journal Personality and Social Psychology Bulletin found that when we intend to do something, our brain creates a false memory of completing the task, which is why we get so baffled afterward.

In the July 16 study, researchers from the University of Illinois at Urbana-Champaign conducted five experiments to figure out why and how people misremember doing mundane, every-day activities like turning off the stove, taking out the trash, or answering an email.

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To test the theory, study participants were told to choose job applicants and either decide to hire them or actually offer them the position. Later on, the study subjects were asked to report whether they'd acted on their decision or only had the intention to do so, an answer many of them could not recollect.

"Intentions and making plans typically improve task execution," Dolores Albarracin, PhD, co-author of the study and a professor of psychology at the University of Illinois at Urbana-Champaign, said in a statement. "We need them to function in society, to realize our goals, and to get along with others."

However, our mind can trick us into blurring intentions with actions. "When we form an intention in the moment such as 'I'm going to sign that form now,' and it's an activity we routinely perform, we want to complete the task when we form the intention," said Albarracin. "Otherwise, we don't actually sign the form. And the reason why is because the thought of wanting to sign the form can be misremembered as actually having signed it."

Man scratching his head confused

The researchers also found that the rate of misremembering increased when the subjects' physical movements and mental criteria mirrored the steps they'd take to actually finish the chore. For instance, if you're on your phone and intend to text someone back, the similar keystrokes of scrolling through social media or typing a note could deceive your brain into believing you answered the message already. Likewise, the physical act of closing the door behind you when you leave the house could trigger the idea that you had locked it too.

Albarracin adds that the more trivial or routine the task, the more likely it is that you'll forget if you've done it. According to the study, the best way to avoid this conundrum is to monitor your actions using a to-do list or some other easy tracker. And for more ways you can train your mind, check out these 15 Games That Will Keep Your Brain Sharp.