Years ago, a friend’s husband asked to have a sexual relationship with me, and I declined. I was upset but not surprised at his proposition; it was common knowledge in our group of friends that he was regularly unfaithful to his wife. Shortly thereafter, he groped another woman at a party in front of a number of people. His wife defended him against our friends opprobrium, saying that she believed him that it had never happened.

As a psychotherapist, I have learned that it is not unusual for people to believe someone, even when they have substantial proof that the are being lied to. Examples include parents who believe that their children are not taking drugs, even after finding a stash in the child's sock drawer; lovers who insist that their partner is faithful despite unfamiliar underpants in the laundry; and business partners who believe that financial losses are for some unexplained reason other than that their best friend is stealing from them.

Why do we continue to believe someone, even when we have rational and substantial evidence that they are lying to us?

One reason is that we have trouble reconciling the fact that someone is lying with what we perceive as expressions of honesty. In his book "Telling Lies," Dr. Paul Ekman, a groundbreaking researcher on lying, writes that most of us cannot tell from someone’s facial expression or body movements whether or not they are telling the truth.

Ekman also found that we want to believe that someone is telling us the truth, especially when that person is emotionally or psychologically important to us. It is painful to believe that someone we care about or trust is lying to us, as is knowing that we cannot trust them.

Denial of reality, or not crediting something that we know is true in some part of our brain, is a way we unconsciously protect ourselves from this pain. In his book "Emotional Bullshit," Dr. Carl Alasko writes that denial “ignores or minimizes an essential fact.”

According to literature put out by the Mayo Clinic, “Refusing to acknowledge that something is wrong is a way of coping with emotional conflict, stress, painful thoughts, threatening information and anxiety.” With denial we can reassure ourselves that everything is okay, even when it is not. The reassurance can give a frightened psyche time and space to work on possible solutions, which is harder to do when you are in a state of panic, anxiety or dread.

Sometimes the comfort of believing someone is the solution to their lies, as it was with my friend whose denial allowed her to stay with her husband. Another woman once told me she had consciously decided, “My husband always comes home to me. I’d rather have that than not have him at all.”

However, denial also has negative consequences: If we don’t recognize a problem, we cannot solve it. When parents find clear proof that a pre-adolescent child is drinking alcohol or doing drugs, for example, denying the evidence can be highly destructive. (Of course, it is important not to make unfounded or untrue accusations, but it is equally important that a child know that you will not simply hide from painful truths.) A young person who is drinking or doing drugs needs parental guidance and a failure to acknowledge this need might make everyone feel better in the short term but create difficulties in the long term.

In other cases, children who are sexually assaulted by an adult are not always believed by other adults. It is sadly common to hear stories of some mothers accepting lies told by boyfriends, husbands and siblings over the truth told by a child. For a variety of reasons, they may not have the emotional strength to respond in any other way. Sometimes mothers are more afraid of the offender than of the offense. Or, they may have been molested or otherwise hurt as children themselves, or feel incapable of caring for their children on their own. Often, they feel that their family would be much worse off if they act on their child’s behalf. They come to feel like their only psychological choice is to believe the lie.

In business as well, it can be hard to accept that a trusted colleague is doing something underhanded, so we accept their lies until the damage is done and undeniable. Such denial of truth can hurt many people, including colleagues, employees, customers and clients. In the worst-case scenario, accepting lies can destroy a business and cause untold harm to numerous individuals.

We believe lies when we feel too vulnerable to allow the truth and its consequences to manifest in our lives. When truth does emerge, we often feel terribly betrayed and we can lose faith in our own ability to make good judgments. To protect against this pain, we sometimes continue lying to ourselves long after reality seems unavoidable.

I am no longer in touch with the woman whose husband came on to me, so I do not know if she is still with him — but I know other couples who have stayed together despite lies ranging from infidelity and finances to addictions and work. I also know men and women who have left relationships when they discovered even small lies, because they could no longer trust the other person. The decision is almost always an effort to find a balance between caring and self-esteem.

If you think that you are accepting someone's lies instead of facing them, talk to someone who will not judge you, like a mental health provider or a mentor who can be neutral and unbiased. They can help you start to feel safe enough to take a step toward a better balance. It is important to remember, however, that accepting lies is self-protection, not a sign of immorality or weakness.

With friends, colleagues and loved ones, it is important to remember that it can take time and work for them to develop the capacity to face the truth. Getting angry or pointing out reality as you see will not move someone out of their denial. It is important to acknowledge that you have a different perspective while clarifying that you are not judging them. Let them know that you are ready and willing to talk about your perspective if they would find that useful. Although they might reject you now, they might turn to you for support in the future.