If you have ever lost weight on a diet only to gain it all back, you were probably as perplexed as you were disappointed. You felt certain that you had conquered bad eating habits—so what caused the backslide? New research suggests that you may have succumbed to a cognitive distortion called restraint bias. Bolstered by an inflated sense of impulse control, we overexpose ourselves to temptation and fall prey to impulsiveness.

Northwestern University psychologists first asked a group of smokers to take a self-control test. Unknown to the par­ticipants, the test was a pretense to randomly label half the group as having high self-control and half as having low self-control. After hearing their supposed result, participants played a game that involved watch­ing the 2003 movie Coffee and Cigarettes while challenging themselves with one of four levels of temptation, each with its own cash reward. They could keep a cigarette unlit in their mouths (for the most money), unlit in their hand, on a nearby desk or (for the lowest reward) in another room. Participants earned a prize only if they avoided smoking for the entire 95-minute film.

Smokers told that they had high self-control exposed themselves to significantly more temp­tation than their counterparts—opting on average to watch the movie while holding a cigarette—and they failed to resist lighting up three times as often as those told they had low self-control.

“Restraint bias offers insight into how our erroneous beliefs about self-restraint promote impulsive behavior,” says lead author Loran F. Nordgren of Northwestern’s Kellogg School of Management. “It helps us to understand puzzles in addiction research such as why recovered addicts often relapse after they have broken free of withdrawal symptoms.” The lesson? When you’ve made progress avoiding your indulgences and that little voice in your head tells you it’s okay to start exposing yourself to temptation again­—ignore it.