DIANA ODRASSO, a 32-year-old film coordinator from Palm Beach, Florida, always considered herself a stellar conversationalist. But for years, she was oblivious to her annoying habit of cutting off people mid-sentence with this rapport-killing phrase: "No, I know." She was, in fact, a serial interrupter. No surprise, her penchant to talk over people didn't score points with colleagues and friends.

Odrasso admits she was far from Miss Popularity among her coworkers on the film festival circuit. Even worse, she lost many friendships and had no idea why—until a roommate intervened. "She told me that I came across as a know-it-all," Odrasso says. "At first, I felt deeply hurt. But my roommate helped me understand that I was being perceived as self-righteous and rude, like I already knew everything."

Before you label Odrasso as singularly clueless, consider this: "To one degree or another, most of us have blind spots about our own behavior," says Michael Patterson, an adjunct professor at Pepperdine University's Graduate School of Education and Psychology and coauthor of a new book about self-defeating behaviors, Have a Nice Conflict. These blind spots make it easy to find fault in others when things don't go our way—say, to blame our flawed parents, our crummy bosses, the entire world!—and prevent us from seeing that often the person standing in our way of happiness and success is the person staring back at us in the mirror. As the workplace becomes more competitive and relationships become more complicated due to the whims of modern life, the stakes are higher than ever.

Why are so many of us unaware of our own behavior? Our fast-paced culture is partly to blame, argues Susan Cain, author of the recent buzz-worthy book Quiet: The Power of Introverts in a World That Can't Stop Talking. "It is deeply ingrained in this society to prefer action over contemplation," she says. In today's world, more people are acting (and texting and tweeting) first, and asking questions later—or never.

According to social psychologists, there's another, even deeper reason: Humans are programmed to see others more clearly than they see themselves—a phenomenon called actor/observer differences. "We read situations differently depending on whether we are the actor or the person watching," says Heidi Grant Halvorson, a motivational scientist at Columbia University Business School, who writes the blog The Science of Success. While others can clearly see that you frequently interrupt conversations or get red-faced and sweaty arguing a point, it's easier for you to ignore or rationalize your behavior, Grant Halvorson says. "You have access to so much information that others don't, like your past experiences, your beliefs about your own abilities, your fears and insecurities. All that extra data affects your interpretation of what you do—so self-defeating behaviors make more sense and seem more reasonable to you."

Often, many individuals have problems identifying their own negative behavior because it is rooted in a trait they're proud of. Have a Nice Conflict tells the story of John Doyle, a fictional sales manager who represents the many people Patterson sees in today's workplace who undermine their own success with unconscious behaviors. Doyle considers himself a model employee—conscientious, diligent, with a strong record—yet is repeatedly passed over for promotions. He hadn't realized that what he considered one of his best assets—his "take-charge attitude"—was considered abrasive by others. "A lot of our behavior is driven by a motivation to achieve a sense of self-worth, to feel good about ourselves, to contribute," says Patterson. "But when taken to the extreme, these strengths can turn into weaknesses."

TAKE LANA CASTLE, who admits that she doesn't ever apologize—and insists that there's a perfectly acceptable reason. "At the end of the day, I am always a little bit right," she says. Castle, 38, from Queens, New York, claims that her best qualities—impressive organizational skills, memory, and problem-solving ability—help explain why she is rarely, if ever, wrong. After her husband told her she was obnoxious for refusing to apologize, Castle says, "Now I try to be a little more humble, a little less know-it-all. But it's tough ... I am usually right-ish!" Castle's difficulty in categorizing this as a fault is not uncommon. "It can be very hard to see this trait in yourself," says psychologist Judith Sills, author of Excess Baggage: Getting Out of Your Own Way. "It can be considered a 'brag' when, in fact, it's a blind spot."

Just as Castle was lucky enough to have someone point out her flaw, Amy Spencer also benefited from a loved one telling her how she was being, well, a jerk. Spencer, the author of the new book Bright Side Up: 100 Ways to Be Happier Right Now, a lifelong optimist, and a relationship expert, is usually not on the receiving end of criticism about her interpersonal skills. But, she admits, "My friend told me if I didn't get my way about something, I'd say, 'Whatever, no big deal' or some other passive-aggressive brush-off instead of explaining that it actually was a big deal for me."

What would lead the author of a book about happiness to be so brusque and unpleasant? "I don't want to make anyone feel bad for not doing something I want them to do. But my solution didn't work because they could read my tone and know I wasn't OK." Spencer's actions were interpreted as sour grapes, though she was striving to be a people-pleaser. "Problems often arise in our relationships because people cannot see our good intentions," says Patterson. "The way our behavior makes them feel can be a turnoff and is a primary source of interpersonal conflict."

So how do you know if you're getting in your own way? First, look for a pattern of setbacks—big or small—in your life. "If at work you're not promoted and you should have been; or you want a relationship and it's been years since you've had a second date, something's wrong," says Spencer. "Once you've run out of the excuses that outside factors are to blame, look to your behaviors." On a piece of paper, write down what has gone wrong in the past month or year that has blocked you from getting what you want. Remember what other people have said about your behavior and even ask for feedback from someone you trust—look for trends. "Seeing past one's own blind spot is a big step to getting over it," says Sills.

The next step: reversing the negative behavior. Spencer, who no longer writes things off as "no big deal," says, "Changing how you act is like practicing the piano. The more you do it, the better you become." That kind of determination was exactly what it took for Anita Smith to stop being a rabble-rouser at work. You know the one: While everyone else is mildly disgruntled over a new policy or memo, she is worked up, sending irate e-mails and airing her frustrations to anyone who will listen. One day her emotional pot boiled over. When a coworker made an offensive remark, Smith lunged at him. "Then others held me back, so I kicked my leg up, which inadvertently led to my sandal flying at him. As it was happening, I thought, I am acting crazy—but I couldn't stop."

The 37-year-old magazine writer got a wake-up call that she brought to her next position. "Every day when something frustrating happens, I tell myself I can't always react and I can't allow people to have this much power over me." Although she never had a meltdown like the last one, Smith says it is a daily struggle to remind herself not to revert to past behavior.

"Reminders are good," says Grant Halvorson. "When you catch yourself thinking, I'm not good at this, think, I'm not good at this yet, but I will be." Smith is no longer the loose cannon whom others snicker about in the conference room. And when she recently saw a coworker lose her cool, she thought, "That used to be me. It was like looking in a mirror at someone I no longer was."

Clear Your Way

Think you might have a few self-defeating habits of your own? Figure out your unintentional behaviors and start breaking through with these easy steps:

1. Ask for an honest assessment. Since it's so hard to get out of your own entrenched mode of thinking, ask people you love and trust—your mom, husband, boyfriend, best friend—to help you identify problem behaviors.

2. Don't get defensive! It's hard to hear constructive criticism, but if you do, you'll be one step closer to making a positive change.

3. Live your ideal life—for 10 minutes a day. "In a perfect world, you don't have annoying behaviors. If you picture yourself wanting to be in a loving relationship, practice being a loving person," says author Amy Spencer. "Do something simple: Buy your friend a little gift, give a good hug, love and adore someone to establish the pattern of being who you want to be."

4. Be patient with yourself. The brain will fold itself around an idea and take a long time to straighten out, says motivational scientist Heidi Grant Halvorson. "Too often, people think, I've been trying something new for a month and things are still the same, so I guess I can't change." Plan what you're going to do differently in order to make a new behavior automatic.

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