Some personality traits are just likable. Agreeableness, for example, is marked by kindness and warmth — who could object?

But although psychologists know a fair amount about how personality traits are generally perceived, they know a lot less about how a person's own personality influences how they handle the personality traits of others. Now, a new study finds that people with dysfunctional traits such as narcissism and antagonism are more tolerant when they run into others who share those troublesome traits.

People's tolerance of such traits might be one reason that personality disorders can be difficult to treat, said study researcher Joshua Miller, a psychologist at the University of Georgia.

"Psychopathic and narcissistic individuals, they understand they are more antagonistic" than other people, Miller told Live Science. "They just don't think it's problematic for them." [7 Thoughts That Are Bad For You]

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A 2014 study in the journal Personality and Individual Differences had found that despite their preference for being in the spotlight, people with higher levels of narcissism —meaning they had an outsize sense of their own self-importance — are actually more accepting of narcissism in others than people low in narcissism are. Prompted by that study, Miller and then-doctoral student Joanna Lamkin decided to study a broader array of personality traits.

In their first study, the researchers recruited 218 college students and surveyed them to determine to what extent they had certain personality disorder traits, including narcissism, antagonism (a dislike of others and a willingness to use people for one's own ends), psychoticism (hostility and aggressiveness) and disinhibition (lack of impulse control). In the second study, 198 students completed surveys on their own levels of general personality traits, not just maladaptive ones.

In both cases, the participants then waited 10 days before coming back for a second survey, to rate how they felt when they encountered those traits in other people. The waiting period was meant to limit people's biases — if you just rated yourself high on a certain trait 5 minutes before, you'd be unlikely to declare yourself against that trait in the next survey, Miller said.

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The consistent finding, Miller said, was that people were more positive toward traits they themselves had — whether those traits were personality disorder traits or more general personality traits.

"If you describe yourself as neurotic, there is a correlation with you saying that you like that trait," Miller said. "It was strongest in the trait we're most interested in, antagonism."

Interestingly, though, the preference of antagonistic people for antagonistic traits wasn't so simple as liking those other traits. In fact, people whose own levels of antagonism were higher than the average rated the trait as 2.52 on a five-point scale, on average. That's on the low side of likability, but still far more forgiving than non-antagonistic people, who rated the trait at 1.6 in likability, on average.

"Antagonistic people don't really like antagonism, and neurotic people don't really like neuroticism, and introverted people don't really like introversion," Miller said. "They're just more tolerant of it. They don't rate it as strongly negative as people who don't have those traits." [Top 10 Controversial Psychiatric Disorders]

The tolerance may explain why psychologists have found that people with personality disorders are slightly more likely to marry or befriend people with similar traits, Miller said. These people don't seek out other narcissists or psychopaths, he said, but they may shrug off the bad behavior of people they meet who have these traits.

There are questions remaining, Miller said. For example, some research has found that narcissists are often initially likable, but that people tend to become more and more negative about interacting with them over time. Likewise, Miller said, "there is data that shows that when two antagonistic people get together, as you might surmise, boy, that's going to be a really big, unpleasant interaction." In a study where people had to interact with others high in their own dysfunctional traits over time, the results might turn out differently.

Ultimately, though, people are aware of their own personality traits and might have a hard time disavowing such an integral part of themselves, Miller said.

"Personality disorders are relatively stable," Miller said. "Not unmalleable, but not the easiest thing to change, and we don't have a lot of great therapeutic approaches to changing really severe personality disorder. This might explain why they don't want to change."

The findings appeared March 4 in the Journal of Personality.

Editor's note: This story has been corrected from the original version. The researchers used a five-point scale in their study (not a seven-point scale).

Original article on Live Science.