For years she hid the credit card bills from her husband: The $2,500 embroidered coat from Neiman Marcus. The $900 beaded scarf from Blake in Chicago. A $600 pair of Dries van Noten boots. All beautiful items, and all perfectly affordable if she had been a hedge fund manager or a Google executive.

Friends at first dropped hints to go easy or rechannel her creative instincts. Her mother grew concerned enough to ask pointed questions. But sales clerks kept calling with early tips on the coming season’s fashions, and the seasons kept changing.

“It got so bad I would sit up suddenly at night and wonder if I was going to slip up and this whole thing would explode,” said the secretive shopper, Katharine Farrington, 46, a freelance film writer living in Washington, who is now free of debt. “I don’t know how I could have been in denial about it for so long. I guess I was optimistic I could pay, and that I wasn’t hurting anyone.

“Well, of course that wasn’t true.”

Everyone is in denial about something; just try denying it and watch friends make a list. For Freud, denial was a defense against external realities that threaten the ego, and many psychologists today would argue that it can be a protective defense in the face of unbearable news, like a cancer diagnosis.

In the modern vernacular, to say someone is “in denial” is to deliver a savage combination punch: one shot to the belly for the cheating or drinking or bad behavior, and another slap to the head for the cowardly self-deception of pretending it’s not a problem.

Yet recent studies from fields as diverse as psychology and anthropology suggest that the ability to look the other way, while potentially destructive, is also critically important to forming and nourishing close relationships. The psychological tricks that people use to ignore a festering problem in their own households are the same ones that they need to live with everyday human dishonesty and betrayal, their own and others’. And it is these highly evolved abilities, research suggests, that provide the foundation for that most disarming of all human invitations, forgiveness.

In this emerging view, social scientists see denial on a broader spectrum — from benign inattention to passive acknowledgment to full-blown, willful blindness — on the part of couples, social groups and organizations, as well as individuals. Seeing denial in this way, some scientists argue, helps clarify when it is wise to manage a difficult person or personal situation, and when it threatens to become a kind of infectious silent trance that can make hypocrites of otherwise forthright people.

“The closer you look, the more clearly you see that denial is part of the uneasy bargain we strike to be social creatures,” said Michael McCullough, a psychologist at the University of Miami and the author of the coming book “Beyond Revenge: The Evolution of the Forgiveness Instinct.” “We really do want to be moral people, but the fact is that we cut corners to get individual advantage, and we rely on the room that denial gives us to get by, to wiggle out of speeding tickets, and to forgive others for doing the same.”

The capacity for denial appears to have evolved in part to offset early humans’ hypersensitivity to violations of trust. In small kin groups, identifying liars and two-faced cheats was a matter of survival. A few bad rumors could mean a loss of status or even expulsion from the group, a death sentence.

In a series of recent studies, a team of researchers led by Peter H. Kim of the University of Southern California and Donald L. Ferrin of the University of Buffalo, now at Singapore Management University, had groups of business students rate the trustworthiness of a job applicant after learning that the person had committed an infraction at a previous job. Participants watched a film of a job interview in which the applicant was confronted with the problem and either denied or apologized for it.

If the infraction was described as a mistake and the applicant apologized, viewers gave him the benefit of the doubt and said they would trust him with job responsibilities. But if the infraction was described as fraud and the person apologized, viewers’ trust evaporated — and even having evidence that he had been cleared of misconduct did not entirely restore that trust.

“We concluded there is this skewed incentive system,” Dr. Kim said. “If you are guilty of an integrity-based violation and you apologize, that hurts you more than if you are dishonest and deny it.”

The system is skewed precisely because the people we rely on and value are imperfect, like everyone else, and not nearly as moral or trustworthy as they expect others to be. If evidence of this weren’t abundant enough in everyday life, it came through sharply in a recent study led by Dan Ariely, a behavioral economist at the Massachusetts Institute of Technology.

Dr. Ariely and two colleagues, Nina Mazar and On Amir, had 326 students take a multiple-choice general knowledge test, promising them payment for every correct answer. The students were instructed to transfer their answers, for the official tally, onto a form with color-in bubbles for each numbered question. But some of the students had the opportunity to cheat: they received bubble sheets with the correct answers seemingly inadvertently shaded in gray. Compared with the others, they changed about 20 percent of their answers, and a follow-up study demonstrated that they were unaware of the magnitude of their dishonesty.