A new study finds that when couples sign on to do something together — start a savings account, diet, get fit and so on — their level of commitment defaults to the least-motivated member of the pair. A lot of people probably think the more conscientious partner would set a good example for and inspire their boyfriend, girlfriend or spouse, but it turns out they’re not the one wielding the primary influence in these situations.

“Self-control is essentially a social enterprise,” writes Hristina Dzhogleva, an assistant professor of marketing at Boston College and lead author of the new paper. In a series of experiments with both real couples and lab simulations, the researchers found that the people with higher self-control tend to cave and give into the more indulgent preferences of their partners in order to keep peace in the relationships.

Given that opposites attract, Dzhogleva points out, it’s likely that there are a lot of couples out there with this dynamic of mismatched motivation levels.