For this study, a team of organizational psychologists out of Europe conducted two studies with 214 employees. Over the course of 1,317 workdays, they asked workers to keep track of their sleep quality, mood, and work engagement. Due to previous theories about the role of willpower (defined in this case as the ability to control impulses, emotions, and desires) on workplace performance, they also noted participants’ theories about willpower.

Unsurprisingly, the researchers found that poor sleep negatively affected workers’ emotions and drained them of motivation, harming their ability to stay on task at work. However, those who believed that their willpower was unlimited fared better the next day. Compared to the employees who told themselves they had a limited reserve of focus and willpower, those who were more confident that they could resist distractions and remain focused—even after poor sleep—were less likely to struggle cognitively.

“Believing that your willpower is unlimited helps you to sustain your effectiveness at work particularly on days with a lack of sleep,” lead researcher Wladislaw Rivkin, Ph.D., said in a statement.

Beyond being more effective workers, Rivkin’s team also found initial evidence that those who believed in unlimited willpower had better mood and vitality overall following a period of poor sleep.