It may be time to start seeing that morning cup of coffee as half full, not half empty. According to new research from Penn State University, worrying over how stressful your day is going to be may undermine your cognitive abilities and make it more difficult to navigate whatever you’re anticipating.

The study, published in the Journals of Gerontology: Psychological Sciences, found that when participants woke up thinking the day would be stressful, their ‘working memory,’ that is, the brain’s ability to learn and retain information even when we’re distracted, suffered later in the day. Which means the expectation of stress affects working memory regardless of whether we actually later experience something stressful.

“A reduced working memory can make you more likely to make a mistake at work or maybe less able to focus,” explains study author Martin Sliwinski, PhD, director of Penn State’s Center for Healthy Aging. “Also, looking at this research in the context of healthy aging, there are certain high stakes cognitive errors that older adults can make. Taking the wrong pill or making a mistake while driving can all have catastrophic impacts.”

The study involved 240 people from different racial and economical backgrounds. Over the course of two weeks, participants answered questions seven times a day, via a smartphone app. In the morning, participants were asked whether they expected the day to be stressful. At five other points during the day, they recorded current stress levels. And at night, they were asked about their expectations for stress on the following day. Participants were also asked to do a working memory task five times throughout the day.

While a lab study may have limited variables that could influence findings, the use of smartphones enabled a more authentic analysis of stress in real life, says study author Jinshil Hyun, a doctoral student in human development and family studies.

“Having the participants log their stress and cognition as they went about their day let us get a snapshot of how these processes work in the context of real, everyday life,” Hyun says. “We were able to gather data throughout the day over a longer period of time, instead of just a few points in time in a lab.”

Researchers found that while more stress anticipation lead to poorer working memory later in the day, stress anticipation from the previous night did not affect working memory.

“When you wake up in the morning with a certain outlook for the day, in some sense the die is already cast,” says Sliwinski. “If you think your day is going to be stressful, you’re going to feel those effects even if nothing stressful ends up happening. That hadn’t really been shown in the research until now, and it shows the impact of how we think about the world.”