Why Some People Lie to Their Partners So Often

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People in a close, committed, relationship believe that they can implicitly trust each other to be honest and truthful. In fact, this seems like a foundational assumption that is basic to the entire idea of intimacy. Yet, researchers have found time and time again that people lie to their partners. Some of these lies are to make liars look better (self-focused lies) and some are intended to protect the partner (other-focused lies).

Who Is Most Likely to Lie to Their Partner and Why?

When you think about the difference between self- and other-focused lies, you can probably understand that some people lie because they think their partner will be better off not knowing the truth. After all, would you tell your partner that one of your relatives really can’t stand them? This type of other-focused lie may come out of a desire to protect your partner’s (and maybe the relative’s) well-being. However, what about overstating the value of the “deal” you got on a concert ticket (for yourself)? Might you want to preserve your image as a person who’s a great negotiator?

According to University of Kassel’s Nina Reinhardt and Marc-André Reinhard (2023), one-third of romantic partners engage in both types of deceptive tactics. The authors believe that the personality trait behind this is “honesty-humility.” This quality refers, much as its name suggests, to the tendency to stick to the truth. The “humility” piece refers to the tendency to avoid self-aggrandizement. A related quality, as Reinhardt and Reinhard point out, is “propriety,” or behavior that upholds moral standards.

Maintaining that “every kind of a lie violates the openness and authenticity people value in their relationships,” the research team decided to plumb the depths of people’s willingness to lie across a series of 11 separate experiments. The constant factor across these experiments was their simultaneous measurement of honesty-humility (adding honesty-propriety in some), but the studies varied in their scope and approach.

In the first seven studies, participants reported in an online format their frequency of lying in romantic relationships, both present and past. Those low in honesty-humility engaged in both self- and other-focused lies; their high-scoring counterparts both were more honest but also saw their partners as being honest, too.

The eighth of these studies used a diary format in which participants recorded the frequency of their daily lies to their partner. Across the five days in which they tracked their lies, participants reported an average of 27 percent in which they lied; in other words, every fourth interaction they had with their partner. Again, though, not everyone did so. Those low in the honesty-humility personality trait turned out to be the worst culprits.

How Far Will a Liar Go to Deceive Their Partner?

You might imagine that these daily, perhaps innocent, lies aren’t too much to worry about. In fact, being “honest” with yourself, maybe you can think of a few fibs from the last couple of days that you’ve conjured up,

This is now where the Kassel U. study becomes interesting. In the final three experiments, the research team instructed participants to behave in deceptive ways that would benefit them financially but at a cost to their partner. See what you would do in these situations:

• Situation 1: Forward a deceptive email about the nature of the study to your partner to double your own take for participating. Claim that the study was about ways to improve the quality of sleep rather than as a study of personality (56 percent of participants did this).
• Situation 2: Cheat at an anagrams task against your partner to earn more money (24 percent of the participants did this).
• Situation 3: Cheat in a dice-roll task while playing against your partner to earn more money. (The expected chance of being right in a dice roll is 3.5; participants reported a mean of 4.3).

As you can see, not everyone lied, but a reasonably high percentage did. Turning to personality as a predictor of lying, it was those low in honesty-humility who made decisions that would benefit them and not their partners. “Exploitation” within this personality trait seemed to play the largest role above and beyond simple dishonesty. In only one of the 11 studies did honesty-propriety prove to have the same predictive power.

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It’s clear that many people, but not everyone, lie to a romantic partner. Finding out who’s more likely to do so could be worthwhile if you’re still in a formative stage with your partner, but perhaps not quite as practical if you’re already committed to a long-term relationship.

Yet, there’s value in either case to know what some of the danger signs may be. There are four domains to honesty-humility: sincerity, fairness, greed avoidance, and modesty (the names of the domains are self-explanatory). Breaking the trait down into its domains can be helpful as you seek guidance on how to read your partner. As the German authors point out, “beyond doing a personality inventory with a (potential) romantic partner—which hardly seems close to reality…” there are signs you can look for.

The authors point to some simple behavioral observations you can make, such as cheating on taxes, being hypocritical with other people, engaging in gambling or speculation, making disparaging comments about other groups, engaging in conspicuous consumption, and, of course, being sexually unfaithful.

If you love your partner and are willing to put up with such potentially unnerving signs, and especially if you are an honest person yourself, you can also use the information from this study as the basis for what might be an uncomfortable but worthwhile conversation. Protecting yourself now will be more than worth the effort of dabbling in this difficult territory.

To sum up, having a partner who doesn’t lie is certainly the most desirable situation of all, but if you don’t, there are ways to find a path back to honest communication.

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