It was a clear summer night in Seattle, and my husband and I had gone to see a concert at a local winery with a couple we were just getting to know. The four of us spread out a picnic blanket, unpacked an assortment of gourmet snacks, and poured wine. Just before the band came on, a dozen hot-air balloons drifted overhead, stunning against the fiery sunset. We oohed and aahed. As our husbands looked on, my new friend turned to me and said, "I've always wanted to go up in a hot-air balloon. Have you ever done that?"

And then, out of my mouth, flew the lie. "Yes."

My cheeks flushed as she smiled in amazement and peppered me with questions. "What was it like? Was it fun? Did they serve Champagne?" I don't remember what I said. I was too stunned by my own deception.

Let me be clear: I had never set foot in a hot-air balloon. Never sailed among the clouds or felt the wind in my hair 1,000 feet above the ground. As the lie smoldered in me that evening, I analyzed dozens of back-out strategies and explanations ("I meant to say that when I worked for a cruise line, I helped people book hot-air-balloon tours, but I never actually went up in one"). In the end, none seemed right. So I kept my mouth shut. I felt guilty and ashamed. The lie, as random as it was, suddenly had power over me.

Today, more than a decade later, it still does. It is the one niggling blemish on my otherwise spotless sense of integrity. What compelled me—the girl who, after taking her first sip of alcohol in high school, immediately confessed to her parents—to blurt out such a trivial untruth? Can I really consider myself an honest person if I could lie so easily about something so silly?

When I put these questions to psychologist Robert Feldman, PhD, dean of the College of Social and Behavioral Sciences at the University of Massachusetts, Amherst, he tells me, "You're a terrible person!"—then laughs. "You acted in a very human way," he says. "That probably wasn't the only lie you told that night. You might have said, 'I feel terrific' or 'You look great,' when your friend didn't look that great. Lying is a natural part of human interaction." Research suggests that by the age of 3, most children understand the short-term benefits of deception to avoid trouble; according to one study, adults estimate they tell roughly 13 lies a week. When I polled my friends about their most recent untruths, one admitted that she'd fibbed to an acquaintance about her plans to attend graduate school at Harvard (she'd been accepted but decided not to go), and another confessed that she'd inflated the total page views of her Web site when making small talk with a stranger in line at the bank.

These misrepresentations, like my own, are classic make-yourself-look-better lies. Feldman says they aren't technically white lies—which are told to spare someone else's feelings; instead, they're what he refers to as social lies. "New acquaintances know nothing about us, so it's much easier to present ourselves in ways that make us more appealing or likable, since the chances of getting caught are low," explains Feldman, who points to a study he led in which he found that during ten-minute conversations with strangers, 60 percent of people lied, on average, two to three times. While the majority of the falsehoods were minor (some agreed with the other person's point of view even when they didn't actually share it, for example), others were bolder—one subject lied about being in a rock band, another trumped up her academic accomplishments.

Next: The most troubling thing she found out

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