Saying no to requests you don’t want to follow through on or don’t have time to accomplish is a difficult skill to master. Especially at the office, many people feel compelled to be a “yes man.” But as a video from SUCCESS magazine's Mel Robbins recently highlighted, there’s a pretty easy way to keep yourself from saying yes when what you really need to say is no.

The key lies in saying “I don’t” instead of “I can’t.” In one of several tests included in a study [PDF] by Boston College and the University of Houston first released several years ago, researchers found that volunteers who said “I don’t skip exercise” instead of “I can’t skip exercise” worked out more often.

Regardless of whether you’re talking to yourself or another person, “can’t” suggests that you might want to do something, but aren’t able to; Robbins gives the example of saying "I can't eat cake for lunch." The implication is that in another set of circumstances, you could. But when you say “I don’t” ("I don't eat cake for lunch"), there’s no room for debate. It’s a hard-and-fast rule that you set for yourself.

The researchers write that “using the word ‘don’t’ serves as a self-affirmation of one’s personal willpower and control in the relevant self-regulatory goal pursuit, leading to a favorable influence on feelings of empowerment, as well as on actual behavior. On the other hand, saying ‘I can’t do X’ connotes an external focus on impediments.”

See more in the video below:

[h/t SUCCESS]