When certified nutrition specialist and personal trainer Jay Nixon meets with new clients for the first time, he typically hears the same opening line: “I’ve tried everything to lose weight, but I always gain it back.” And in almost every case, the reason is the same, he says: “They didn’t change anything psychologically.”

In his recent book The Overweight Mind, Nixon argues that only about 20% of weight-loss success is mechanical—or what you eat, and how often (and intensely) you exercise. The rest, he believes, is mental: “Getting a handle on [your] mindset is what leads to long-lasting results.”

Psychological change might actually feel more daunting than adding an extra serving of veggies to your plate. But Nixon promises it’s easier than you think. In fact, it can be as simple as changing your vocabulary.

There are three short words he wishes everyone would ban when it comes to exercise and diet: can’t, won’t, and don’t. “Those words wrap around everything having to do with people’s physical condition, to the point that they don’t even realize they’re saying [them] anymore,” he says. “They don’t have awareness around how often they use these words.”

Using them less often, he says, can have a direct impact on your fitness and weight-loss success. Here, a few examples of how you can flip the script on all that negative talk.

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“I don’t like vegetables”

Nixon has found that in the context of food and fitness, people often say “don’t” because of a negative past experience. For example, if someone says he doesn’t like vegetables, it could be because eating kale once made him feel sick. Or if someone says she doesn’t run, it may be because she once suffered an injury from running.

When his clients use the word “don’t,” he reminds them that “old experience doesn’t need to dictate current behavior.” Then he helps them take small steps to turn those don’ts into dos. For example, he might encourage the non-runner to simply move as quickly as she can. Odds are, after a few weeks, she’ll have naturally picked up the pace.

“I can’t do 10 push-ups”

“I get clients to reframe that sentence,” Nixon says. Instead of declaring you can’t do 10 push-ups, remind yourself that you can do 1 push-up. “Every day, reapply it,” he says. So the next day tell yourself, I can do two push-ups, and keep going until you hit your goal.

“I won‘t wake up early to work out”

People who use “won’t” in a sentence like this have convinced themselves the statement is a fact, says Nixon. But the statement only feels true because of how often the person has repeated it. Again, you need to reframe the thought: Think about what you will try–say, two early mornings a week–and then focus on how to make that behavior stick.

It can help to create a sense of accountability for yourself, Nixon suggests. “I try to get people to form a sort of community,” he explains, whether that means recruiting a workout buddy to meet you at the gym before dawn, or finding a friend on a similar path, who you can share your plans and progress with. Or if prefer to go it alone, start a journal, Nixon suggests. Even writing down what you will do in a journal can keep you honest, he says.

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These reframing tricks will help you stay on track no matter what phrase follows the word “don’t,” “can’t,” or “won’t,” Nixon says. No weight-loss journey is perfectly smooth, he points out. “When we hit roadblocks, we always fall back a little bit. But if you’re working on your psychology, you won’t fall as far.”