Mentally simulating another person’s efforts to use self-control may trick your brain’s “fuel gauge” into mistakenly thinking that your own resources have been depleted, a new study suggests. “We’re not as individual as we might like to think,” says Yale University psychologist Joshua Ackerman. “Often how we understand the world is by relying on the understanding of other people.”

If your friend scratches her eyebrow or crosses her arms, studies suggest, odds are you’ll unthinkingly mimic the gesture. In the same way, research has shown, goals are also contagious: seeing another person pursue a goal—say, thwarting the urge to have one more Girl Scout cookie—automatically activates the same goal in one’s own mind. And neuroimaging studies indicate that mentally simulating another person’s experience triggers the same sensory and emotional brain pathways that are activated when one actually performs the action. For example, watching a video of someone about to cut her finger with a kitchen knife triggers brain areas involved in pain perception.

Ackerman and his colleagues reasoned that if we are wired to treat others’ actions as though they are our own, then stepping into the shoes of someone who is exerting self-control should deplete one’s own mental resources, just as exerting willpower oneself does. They found that sub­jects who took the perspective of a hungry restaurant waiter who had to resist the temptation to eat on the job were more vulnerable to impulse spending than subjects who merely read about the waiter.

In the real world, where no one is instructing you to take another’s point of view, such vicarious effects are most likely when we are around people who are similar to us or whom we like, Ackerman suspects. University of Minnesota psychologist Kathleen Vohs agrees: “The default way of seeing the world is through one’s own eyes. It takes energy and motivation to overcome one’s egocentrism.”

Note: This article was originally printed with the title, "Waning Willpower."