As author A. J. Jacobs told ABC News' David Wright recently, when he decided to spend a year observing the ninth commandment - which he interpreted as Do Not Lie - it was the "worst experience of my life."
Try telling your mate that fat is beautiful.
So you lost the game, 57 to zero, but you played well. Right.
We lie, according to many studies, because we think we have to. Our social graces demand it. Even if we are children.
Adults can excuse a little lying because we're sensitive and don't want to hurt someone's feelings. But kids have it tougher. They have to go through "mental gymnastics" just trying to sort through a batch of mixed signals, Heyman said.
"The big question that motivates me is kids have to figure out the social world," she said. "Unlike a lot of other things, like math, where they get a lot of direct instructions, in the social world they get little direct instruction and the instruction they do get is often completely going to get them in trouble, or it is misleading. They are told never to talk to a stranger, but then they are expected to talk to a stranger in a variety of circumstances or the parents get mad at them if they don't. It's just really confusing."
Or they are told never to lie, and then they get in a whole mess of trouble when they admit that the pool of water near the dog dish really didn't come from the dog. And in most cases, they've probably heard a parent lie just to spare the feelings of a friend. So it's likely that kids learn early of the value of a little white lie.
"Children start lying when they are about two," Heyman said. "Do they understand it's a lie? It gets messy" because growing up is filled with contradictions.
Heyman was around 5 when she caught her parents in what to her was a really big lie. Her kindergarten classmates got into a discussion of the tooth fairy, and as it turns out there were a few cynics in the crowd.
"My parents would tell us all these stories about the tooth fairy and all the things she did and I loved it," she said. "I was very excited about it, and then some of the kids in my kindergarten class were saying there is no tooth fairy. I had to defend the tooth fairy, and the more I talked, the more I realized that it didn't make sense."
So that evening she confronted the Big Guy, old dad.
"I was really sad, and I told him there is no tooth fairy, is there," she added. "Then he told me the truth, and I remember thinking I could never believe what he said again."
A five-year-old cynic? Kids learn early. Maybe there really is no such thing as a little white lie.
But say you will never tell one and you'll be lying.