How you think about willpower and self-control can make a big difference in how much of it you feel you have.

Maybe you have been beating yourself up about the number of days you've skipped your 20-minute walk or because you had mashed potatoes when you ate dinner out. Lighten up. Your self-criticism may backfire, making you less able to muster your willpower and making it even harder to do more of what you need to do for your health, your work and your relationships, a study finds.

If you are struggling to stick with your diet, make it to the gym or be a better parent, don't despair. In fact, you should see despair as the problem, not willpower.

“What matters most is what we think about our willpower,” said Christopher Napolitano, the lead author. “When we view our willpower as limited, it's similar to a muscle that gets tired and needs rest. If we believe it is a finite resource, we act that way, feeling exhausted and needing breaks between demanding mental tasks, while people who view their willpower as a limitless resource get energized instead.”

The University of Illinois study was a test of a measure of willpower, the Implicit Theory of Willpower for Strenuous Mental Activities Scale (ITW-M). The scale asks people to respond to statements about self-control such as, “After a strenuous mental activity, your energy is depleted, and you must rest to get it refueled again.” More than 1,100 Americans and 1,600 Swiss- and German-speaking adults took part.

The idea was to test whether the ITW-M measured the concept of willpower consistently across sexes and different cultures. Napolitano and co-author Veronika Job of the University of Zurich compared participants' scores on the ITW-M questionnaire with their scores on similar assessments that explored their beliefs about self-control, which relates to their ability to rein in their impulses.

They found that there was little variation between men's and women's willpower scores on the ITW-M, and the test results were in line with participants' scores on other measures of self-control. There was one difference: European participants seemed to find willpower easier to come by. Americans were more likely to say they needed to rest and recover after performing mentally taxing activities, while the Europeans reported feeling invigorated. The researchers suspect language differences may have been a factor in these results.

If you are struggling to stick with your diet, make it to the gym or be a better parent, don't despair. In fact, you should see despair as the problem, not willpower. As Napolitano says, “ Your feelings about your willpower affect the way you behave — but these feelings are changeable. Changing your beliefs about the nature of your self-control can have positive effects on development, leading to healthier behaviors and perceptions of others.”

The study is published in Psychological Assessment.