"Honesty is the best policy" is no idle aphorism for Mendelson. He's determined to stick to his forthright even at the risk of losing friendships or jobs. When his former employer—a TV network affiliate—assigned him to cull hundreds of news stories from other publications for possible re-use, Mendelson gradually realized much of his labor was going to waste. "Ninety-nine percent of the stories were never used," he says. He approached his supervisor and aired his opinion point-blank. "I told him, 'What you guys are doing is awful—it needs to be fixed,'" Mendelson remembers.

The boss brushed him off, but a higher-level supervisor at the company called, said he'd heard about Mendelson's concerns, and asked for his suggestions on making the story-selection system better. Mendelson admits his policy of radical honesty hasn't always yielded such happy results. "I'm not exactly Mr. Sensitivity. I've cost myself quite a few jobs by telling people what I thought." Like the time he told the hiring committee of a local chamber of commerce they were doing everything wrong.

Though most kids are reared on maxims like "Never tell a lie," people who commit to total honesty in every situation are a rarity. Many of us lie to some degree, typically to avoid provoking conflict in relationships. "People don't want to hear the unvarnished truth—we're putting on weight, the new dress we bought looks terrible," says Robert Feldman, a University of Massachusetts psychologist who studies . "So we learn that it's appropriate to withhold the truth sometimes." Similarly, many people fudge details about their lives ("I wasn't just sitting on the couch. I applied for three jobs today!") to duck the discomfort that comes with not meeting others' expectations.

Truth tellers, however, are committed to honesty regardless of the social repercussions. After Mendelson started a band with some friends several years ago, he confronted them about their failure to pull their weight in promoting the band. "They were slacking. At one concert, I was working the door, I was emceeing, and they were just hanging out. I told them, 'This is B.S.'" The other band members didn't react well to his candor. "I haven't really talked to any of those people since then," he says.

Most religious and philosophical traditions include some version of "Thou shalt not bear false witness," and Mendelson aims to follow that dictate to the letter. "Telling the truth helps me sleep at night with a clear ," he says. But some social scientists believe lying isn't a universal ethical faux pas—it depends on the situation at hand. "People who tell lies are very oriented to other people and what they think," says Bella DePaulo, a psychologist at the University of California at Santa Barbara. Telling "appropriate lies"—like the time you told Aunt Erma you loved the chartreuse pantsuit she got you for the holidays—isn't a sign that you're morally bankrupt. It's a sign you're attuned to her feelings.

Shading the truth has its share of social advantages, so why do a few rare individuals insist on honesty at all costs? In some cases, straight shooters may be a product of the family environment they were raised in, says Victoria Talwar, a developmental psychologist at McGill University in Montreal. In a study examining children's moral development, Talwar found that parents who do not talk about the importance of preserving other people's feelings are likely to raise offspring with a blunt relational style.

Mendelson, however, says his penchant for honesty evolved as a result of a teenage prank that got a little out of hand. "In high school, I made a Web site making fun of everyone at the school—it had a top-10 list of jerks and some funny audio." After word of the site leaked out all over the school, Mendelson eventually decided to admit he was responsible. That experience made him realize it was simplest to stand behind what he believed was true, he says. "I knew I couldn't stay under the radar, so from that point, I decided just to tell the truth about everything."

Many truth tellers opt for honesty because lying seems too complicated or makes them too . Liars have to remember to keep their false stories straight. A University of Portsmouth study found that liars usually pause more often in their speech, for example, and some people blush profusely when they lie. Being a blunt truth teller, on the other hand, "is really easy," Talwar says. "You just tell it as it is."

In some cases, truth telling may be a byproduct of the way the brain is structured. People with , for example, are extremely forthright because they have a limited capacity to understand the social repercussions of their blunt honesty. "My mother had , and she literally could not tell a lie," says Ellen Snortland, a writer and producer in Los Angeles. "After my father died, I asked her, 'Do you ever miss Dad?' She said, 'Nope, I'm glad he's dead.' She didn't say it with malice. It was merely true for her."

Not all truth tellers are scrupulous or socially naive, however; some of them use the truth as a kind of sophisticated bludgeon. "It can be almost a holier-than-thou thing," DePaulo says. "Sometimes people use honesty as an excuse to hurt others. They say something nasty and then say, 'Well, I'm just being honest.'"

"As Emily Dickinson said, 'Tell the truth, but tell it slant,'" DePaulo says. "You can convey what you really mean without being hurtful." But Mendelson's not a big fan of the "tell it slant" approach. The possibility that he might offend a few people doesn't scare him. "I want to tell 100 percent absolute truth, or else I'm wasting my time," he says. "Being able to give people a straight, honest answer is a gift."

Tell the Truth—Tactfully

Adopting a straightforward attitude can change your life and relationships for the better—as long as you use the truth wisely.