When you think of romantic compatibility, you probably think of two people who are a perfect fit and would likely make a great couple.

But what many people misunderstand about compatibility, according to one marriage therapist we recently spoke with, is that it’s not always a good thing.

TheDarkSideofRomanticCompatibility.

First, let’s define what we mean when we talk about compatibility: “Compatibility is a natural, easy way to connect with another person and feel connected,” licensed couples therapist Racine Henry, Ph.D., LMFP, recently told mbg. She points out that two people don’t have to be alike to be compatible, and in fact, compatibility often stems from two people having a mechanism to deal with conflict in areas where they disagree.

“Compatibility in a relationship comes from having a complementary relationship,” she explains, but that’s where things get complicated, too.

According to Henry, just because two people are compatible or have complementary qualities “doesn’t always mean it’s a healthy or positive complement.” Sometimes two people complement each other in ways that might not be in the best interests of one or both people.

For example, she says, “There might be a controlling person who finds a passive partner.” This can potentially help the two work through conflicts—the controlling person will simply override the passive person, who will in turn give in and agree with their partner’s decisions. This means the relationship might be able to continue—but it doesn’t necessarily mean it should.

There are many examples of unhealthy compatibility: Narcissists often seek out an echo chamber, their humble opposite, who they can take advantage of more easily. Someone who doesn’t give much in relationships might do well with someone who doesn’t demand much, masking the former’s selfishness and abandonment issues.

What to Look For Besides Compatibility.

Just because two people are compatible doesn’t mean they’re a good match, and just because a relationship is technically successful doesn’t mean it’s healthy. People can be attracted to people for the wrong reasons, and sometimes people stay in unhealthy relationships simply because they’re familiar or comfortable. In those situations, “compatibility” doesn’t do us much good.

As psychotherapist Ken Page, LCSW, previously told mbg, “We have to cultivate our ability to discern.”

Aside from compatibility, it’s important to check to see if the building blocks of a healthy relationship are in place — things like trust and vulnerability, equal give and take, the ability to nurture yourself and the relationship at the same time, and a sense of true security. According to relationship therapist Jordan Dunn, MFA, L.P., CIRT, a healthy relationship requires a healthy dose of differentiation.

Here’s a complete list of green flags to look for in a relationship. And if you need it, we also have a toxic relationship quiz to help you identify unhealthy patterns.

Bottomline.

While compatibility in terms of personality, values, and lifestyle can certainly contribute to a sustainable relationship, it’s important to realize that compatibility isn’t all good. Sometimes we “match” with someone for the wrong reasons, so we need to be able to look beyond that feeling to see if the relationship is truly serving the needs and overall well-being of the person.