I wish I could do _______, but I can't.
"I can't almost always means I don't want to," says Amy Johnson, PhD, a Chicago psychologist. "I can't allows us to pretend the choice isn't ours," she says. "It feels beneficial in the short term because we don't have to own our preferences or admit that we have a choice in the matter. But Johnson says that habitually saying "I can't" makes people feel disempowered across all areas of their lives. "I tell clients to say 'I don't want to' instead of 'I can't'—even if it's just to themselves. It gives them their sense of power and choice back."

I deserve this dessert...
Or this dress. Or this car. Or...whatever. "I hear this so often," says Johnson. "These lies let us hide from our real feelings with momentary comforts. The problem is, when the comfort wears off, we're left facing the feelings." Johnson once had a client who said she deserved to indulge in rich food after a long day at a job she loathed. "She believed the food was a reward, even though it was wrecking her health and her energy levels," says Johnson. "No one 'deserves' to wake up feeling awful. My client finally came to see that what she really deserved was to work at a job she loved. When her job changed, the desire for the comfort food decreased."

Johnson says another insidious phrase that people use is I need, as in, "I need that new black dress." "If you're alive and surviving without it right now, then you clearly don't need it," she says. "It might sound insignificant, but changing I need to I want is incredibly freeing. I need sets you up to believe that you'll be hurt if you don't get the thing. I want gives you more freedom."

I'm definitely right.
This is one of the most damaging lies we can tell ourselves, says Carol Tavris, PhD, social psychologist, co-author of Mistakes Were Made (But Not by Me): Why We Justify Foolish Beliefs, Bad Decisions, and Hurtful Acts. "It's called the basic bias—the idea that everyone else is biased, but we're not." The belief that you know best and that you've got all the facts prevents you from even listening to evidence that you're wrong—that your memory is wrong, your perception is wrong, your explanation is wrong. It's self-damaging, in that it keeps you stuck within the confines of what you think you know, and, says Tavris, "it also makes you a miserable person to be with."

I have no willpower.
You have some willpower. We all do, says Roy Baumeister, social psychologist and author of Willpower: Rediscovering the Greatest Human Strength. Baumeister discovered in lab tests, though, that willpower is finite—after people used self-control for some tasks, they had less of it for subsequent tasks (so it's probably best not to quit smoking, get organized and go on a diet on the same day.) But he also found that willpower, like a muscle, can be built up over time through regular training. One of his experiments in self-control involved a simple exercise to improve posture. "For two weeks, people tried to stand or sit up straight whenever they thought of it," he says. "Not only did their posture improve, but they showed all-around improvement in self-control, even on laboratory tests that had nothing to do with posture."

I'll never get over it.
"We're not necessarily conscious of how rapidly we recover from adversity," says Richard J. Davidson, PhD, a neuroscientist at the University of Wisconsin, and co-author of The Emotional Life of Your Brain. (You've probably heard of the research on how people who've been paralyzed are about as happy a year after the accident as they were before; same goes for lottery winners who are no happier a year later).

Richard Summers, clinical associate professor of psychiatry at the University of Pennsylvania, tells most of his patients undergoing a crisis "to allow themselves to really feel some of the negative emotion and to trust nature—those emotions have really a finite lifespan and tend to abate over time." That said, he offers a benchmark for people who are grieving. "There's a big spread, and it's important to remember that," he says, 'but a good rule of thumb is that after six months there should be at least some sense of forward motion for the person." If not, professional help may be one answer.

Davidson says that people who are slower to recover from stressful events actually have brains that are wired differently. Fortunately, people have the ability to change their brains' activity patterns. One of the most effective ways to do this, Davidson says, is mindfulness meditation, which boosts activity in the prefrontal cortex, and studies have shown this weakens the chain of associations that keep us obsessing about a setback. He highly recommends a course in Mindfulness-Based Stress Reduction, available on the University of Massachusetts Center for Mindfulness website. But, as with willpower, learning a new language, Jazzercise and so many things in life, the exercises must be done regularly. "To change your brain in any kind of systematic way takes practice," he says, "something there's no substitute for."

I don't judge people.
Sure you do. Researchers from Harvard Business School, who've recently studied how people categorize and perceive others, say that within less than a second, we make what are known as "spontaneous trait inferences." These are remarkably consistent. All over the globe, it turns out, people instantly judge each other on two main qualities: warmth and competence. People who are judged as competent but cold—for instance, a wealthy tycoon—elicit envy or hostility. People who are usually perceived as warm but incompetent (such as elderly people) bring out feelings of pity. We're still judging with our conscious mind when we size people up, adds Michelle B. Riba, MD, MS, clinical professor of psychiatry at the University of Michigan. "Although when we do this, it's ourselves that we're judging, really, more than the other person," she says. "We're trying to figure out how we fit in."

If only I had a million dollars, I'd fulfill my dreams and do_____.
This little self-deluding chestnut? It's disproved every time we see an attorney who aspires to own a pastry shop and bakes cookies to sell on the weekends, or a baker who goes to law school at night. Somehow, though, we are certain—absolutely certain—that we can't take the leap without a financial guarantee or windfall. It's a Truth, we believe, with a capital T. But getting a few friends together and using a workshop exercise from the famed comedy troupe the Upright Citizens Brigade can help convince you otherwise: "It's called 'heightening,' which is one of the fundamental elements of improv," says workshop director Carter Edwards.

"The idea is that the next person must agree with your self-delusional statement and heighten it by adding something funny and absurd to it. 'Right, you can't open a catering business because you need a million dollars, so you have to win the lottery.' Then the next person adds something else, like, 'You can't open a catering business because you have to win the lottery—and see every episode of The Real Housewives first.'" The idea is to continue until the group can't go any further, so that you have to face that your original supposition, the lie you told yourself, is just not viable. "That's the basis of improv," says Edwards, "not to shame, but to support each other and move past what's hanging you up—through humor—so you get at the bigger truth."

More Ways to Tell the Truth

• Martha Beck: How to deal with your darkest secrets
• When is honesty the best policy with your spouse?
• How to recognize your emotional blind spots