People who think they’re less active than their peers—even if they’re logging the same amount of workout time—are more likely to die younger compared to those who perceive themselves as active, according to a new study published in the APA journal Health Psychology.

Researchers from Stanford University analyzed three different data sets that totalled 61,141 U.S. adults. The participants were surveyed between 1990 and 2006, with follow-up data collected in 2011 to calculate mortality rates, according to the study’s press release.

Participants were split into two groups: one group self-reported their activity levels by answering questions about their exercise habits (how often, for how long, how intense, etc.). The other group wore a device that actually measured their activity for a week. All of the participants then shared whether they felt more, less, or similarly active compared to other people their age.

Surprisingly, people perceived their activity levels as being a lot lower than they really were.

This is more than just a strange disconnect between thought and reality: “People who believed they weren’t as active as their peers were 71 percent more likely to die during the study’s follow-up period than were people who believed they had a more active lifestyle,” according to the press release. This was true even after controlling for a variety of factors including age, demographics, medical histories and actual activity levels.

“Most people know that not exercising enough is bad for your health,” Octavia Zahrt, PhD and doctoral candidate at the Stanford University Graduate School of Business, said in the press release, “but most people do not know that thinking you are not exercising enough can also harm your health.”

The placebo effect might be at work here—it’s been shown to have a powerful impact on the link between perception and physical experience. “Following this logic, someone who does not believe that she is exercising enough may get fewer physiological benefits from activity than someone who believes she is exercising enough,” Alia Crum, PhD, assistant professor of psychology and director of the Mind and Body Lab at Stanford University, said in the press release.

Another possibility is that when people think they’re doing less or worse than their peers, they become “depressed, fearful and less active,” the authors said in the press release, which can lead to poor health outcomes.

Zahrt offered a few possible explanations as to why people get stuck in the “I’m not active enough” mentality. One is that if you’re constantly surrounded by exercise fanatics, you might think you’re slacking even if you’re getting plenty of activity, she said in the press release. This can also influence what people think qualifies as exercise, she said: “If you believe that only running or working out at the gym count as real exercise, you may overlook the exercise you are getting at work or at home cleaning and carrying the kids around.”

More research needs to be done to understand the link between perceived activity and life expectancy, and it’s important to note the study showed correlation, not causation. But these findings are an interesting development in how our thoughts may impact our health. “Our research suggests that perceiving everyday activities as good exercise is almost as important as doing the activities in the first place. In the pursuit of health and longevity, it is important not only to adopt healthy behaviors but also healthy thoughts,” Crum said in the press release.

The findings don’t give you license to skip the gym because you told yourself chewing lunch was a good workout, but they’re a good reminder that your overall activity levels go beyond what you do during your workouts. Give yourself credit for taking the stairs, parking farther from the office or chasing after your kids.

Read the press release here.