If you’ve been trying to get your finances in order, one single word can make all of the difference between success and failure. 

What’s the word? It’s “don’t.” People who are trying to change their behaviors, according to author of The Motivation Myth, Jeff Haden, often find themselves needing to say no to themselves. 

In personal finance, it might mean saying no to a big purchase. Or saying no to an expensive meal. Or a flashier car. 

That’s one of the toughest parts of following a process, or creating a new habit, or simply trying something new and difficult: saying “no” to yourself. 

And you end up doing what you didn’t plan to do—or not doing what you planned to do. So what is the best way to say no to yourself? It’s easy: Stop saying “can’t” and start saying “don’t.” 

It works. Science says so. Researchers conducted a study: … Participants were told to set a personal long-term health and wellness goal. When their initial motivation flagged—as initial motivation inevitably does—one group was told to say, “I can’t miss my workout.” Another group was told to say, “I don’t miss my workouts.” (The control group was not given a temptation-avoidance strategy.) 

Ten days later the researchers found: 

• Three out of ten control group members stuck to their goal.
• One out of ten “I can’t” group members stuck to their goal.
• Eight out of ten “I don’t” group members stuck to their goal. Not only was “I can’t” less effective than “I don’t”; “I can’t” was less effective than using no strategy at all. 

Why? According to the researchers, “The refusal frame ‘I don’t’ is more persuasive than the refusal frame ‘I can’t’ because the former connotes conviction to a higher degree…Perceived conviction mediates the influence of refusal frame on persuasiveness.”

If you’re trying to change your financial habits, you might want to bookmark the article about the important difference between “can’t” and “won’t.”