In the 1970s, the gift shop at the Kennedy Center for the Performing Arts was an informal affair. It was staffed by about 300 mostly elderly volunteers, and there were cash drawers instead of registers. The problem was that of the shop’s $400,000 in annual revenue, somebody was stealing $150,000.

Dan Weiss, the gift shop manager at the time who is now the president of Lafayette College, investigated. He discovered that there wasn’t one big embezzler. Bunches of people were stealing. Dozens of elderly art lovers were each pilfering a little.

That’s one of the themes of Dan Ariely’s new book “The (Honest) Truth About Dishonesty.” Nearly everybody cheats, but usually only a little. Ariely and his colleagues gave thousands of people 20 number problems. When they tackled the problems and handed in the answer sheet, people got an average of four correct responses. When they tackled the problems, shredded their answers sheets and self-reported the scores, they told the researches they got six correct responses. They cheated a little, but not a lot.

That’s because most of us think we are pretty wonderful. We can cheat a little and still keep that “good person” identity. Most people won’t cheat so much that it makes it harder to feel good about themselves.

Ariely, who is one of the most creative social scientists on the planet, invented other tests to illustrate this phenomenon. He put cans of Coke and plates with dollar bills in the kitchens of college dorms. People walked away with the Cokes, but not the dollar bills, which would have felt more like stealing.

He had one blind colleague and one sighted colleague take taxi rides. The drivers cheated the sighted colleague by taking long routes much more often than they cheated the blind one, even though she would have been easier to mislead. They would have felt guilty cheating a blind woman.

Ariely points out that we are driven by morality much more than standard economic models allow. But I was struck by what you might call the Good Person Construct and the moral calculus it implies. For the past several centuries, most Westerners would have identified themselves fundamentally as Depraved Sinners. In this construct, sin is something you fight like a recurring cancer — part of a daily battle against evil.

But these days, people are more likely to believe in their essential goodness. People who live by the Good Person Construct try to balance their virtuous self-image with their selfish desires. They try to manage the moral plusses and minuses and keep their overall record in positive territory. In this construct, moral life is more like dieting: I give myself permission to have a few cookies because I had salads for lunch and dinner. I give myself permission to cheat a little because, when I look at my overall life, I see that I’m still a good person.

The Good Person isn’t shooting for perfection any more than most dieters are following their diet 100 percent. It’s enough to be workably suboptimal, a tolerant, harmless sinner and a generally good guy.

Obviously, though, there’s a measurement problem. You can buy a weight scale to get an objective measure of your diet. But you can’t buy a scale of virtues to put on the bathroom floor. And given our awesome capacities for rationalization and self-deception, most of us are going to measure ourselves leniently: I was honest with that blind passenger because I’m a wonderful person. I cheated the sighted one because she probably has too much money anyway.

The key job in the Good Person Construct is to manage your rationalizations and self-deceptions to keep them from getting egregious. Ariely suggests you reset your moral gauge from time to time. Your moral standards will gradually slip as you become more and more comfortable with your own rationalizations. So step back. Break your patterns and begin anew. This is what Yom Kippur and confessionals are for.

Next time you feel tempted by something, recite the Ten Commandments. A small triggering nudge at the moment of temptation, Ariely argues, is more effective than an epic sermon meant to permanently transform your whole soul.

I’d add that you really shouldn’t shoot for goodness, which is so vague and forgiving. You should shoot for rectitude. We’re mostly unqualified to judge our own moral performances, so attach yourself to some exterior or social standards.

Ariely is doing social science experiments and trying to measure behavior. But I thought his book was an outstanding encapsulation of the good-hearted and easygoing moral climate of the age. A final thought occurred to me. As we go about doing our Good Person moral calculations, it might be worth asking: Is this good enough? Is this life of minor transgressions refreshingly realistic, given our natures, or is it settling for mediocrity?