By now you may have heard of Kari Ferrell, the New York administrative assistant who seemed like an average 22-year-old hipster ... until it was discovered that she's a pathological liar on the run from the law.

But Ferrell isn't the first person to make the news for whipping up whoppers, and she won't be the last. But why do liars start spinning yarns in the first place?

Everything But the Truth

Kari's hardly the first con. Esther Elizabeth Reed, for example, maneuvered her way into Ivy League schools and avoided capture for the better part of a decade. In France, Frédéric Bourdin, 30, was able to fool people in more than a dozen countries into thinking he was an abused teenager.

Even though they have to be fairly intelligent and cunning to lie, psychologist Doris Jeanette of the Center for New Psychology in Philadelphia says pathological liars do what they do because they are "massively insecure." They don't think they're good enough on their own, so they formulate fibs to feel better.

"Most liars will lie about anything, even when it is not important and it does not matter," Dr. Jeanette said. "They just say anything because there is no connection with their emotional self."

Are they crazy or calculating? Click here for more.

Insane in the Brain?

That emotional disconnect allows liars to believe their own lies. And that helps them convince others of their untruths.

Michelle from New York, for example, was taken in by a gal pal who curried sympathy with talk of a rough childhood.

"Knowing she had a tough upbringing, I didn't mind grabbing the bill or paying for cabs. I was even entertained by the stories of how she lived in Rome when she modeled for Ford Modeling Agency, that her father was from Rio de Janeiro or that her roommate stole $1,000 in cash from her bedroom," Michelle admits.

Michelle even let it slide when she thought the friend had stolen cash from her. But when she discovered that some of their mutual acquaintances had experienced similar behavior, Michelle confronted the woman.

Liar, Liar, Pants on Fire

The scary part is there seems to be no way to predict who or what will turn someone into a liar.

"I have known poor people who were severely physically traumatized in early childhood who lied and well-educated people who were emotionally traumatized who lied," Dr. Jeanette says. "I have known many who were abused and did not lie, so no, I cannot say from my clinical experience there is a common trauma for liars."

But biology is another story. Scientists at the University of Southern California found that truth twisters have more "white" matter in their brains and less "gray" matter. In English, that means they are more verbal and have less of a moral compass than normal people, which makes faking it a piece of cake after a while.

All in the Family -- or Not

Michelle eventually cut ties with her lying friend. For others, it's not so easy. Beth from North Carolina says her brother has lied about working for a major league baseball team, spying for the government and producing TV shows. She and her sisters haven't spoken to him in two years.

"We say about him, 'If he's talking, he's lying.' He's been that way ever since he could talk and also has a pretty extensive arrest record. However, his ability to con people has prevented him from serving any real time in jail."

Shirley from Pennsylvania says even though her sister-in-law is attractive, intelligent and personable, she lies compulsively. She's fibbed about her occupations and makes up illnesses.

"She will stare right at you and tell you the most fabulous, ridiculous lie, and it's almost like she is daring you to tell her she's lying ... I tried to organize a family intervention, but no one wanted to challenge her." Shirley eventually confronted her sister-in-law on her own and asked her to get help. The two haven't spoken since.

Tell us: Do you know someone who lies constantly? Do you ever call them out on their behavior?