We’ve all heard the story of the good girl who falls for the guy from the other side of the tracks. Sure it’s cliché, but there’s some truth to the “opposites attract” theory—the girl has been sheltered her whole life, and she’s intrigued by the boy’s recklessness, by his entirely different attitude. He introduces her to cigarettes and motorcycles, they run away to get married in secret, they live happily ever after. Obviously.

And I think in general, people are intrigued by what they don’t understand. We find it fascinating to watch others use skills we don’t have—for instance, painting, playing piano, or solving a Rubik’s cube. In this way we are drawn to those different from us. We’re very curious and we like to explore new things; when we find someone vastly different from us, they have a lot to learn from each other.

But do the good girl and the bad boy really live happily ever after? Unlikely. A few months down the road, she’s going to realize she can’t stand her house smelling like smoke. She’s going to want to trade the motorcycle in for something more practical. She’s going to want a little more order in her life than her partner. The marriage won’t last.

This is because there is a big difference between attraction and compatibility. You might call it lust and love, but I think that’s oversimplifying it. Attraction is what brings you together; compatibility is what keeps you together. And two polar opposites might be attracted to one another, but it’s not likely that they’ll stay together long. You have to have something in common in order to maintain a healthy relationship, and there are some cases in which opposites simply cannot coexist. The most obvious are lifestyle conflicts: maybe your religious beliefs aren’t compatible, or one person wants children and the other doesn’t. But to me, some things are far more difficult to reconcile than these lifestyle differences. The biggest is probably humor—if you don’t get each other’s jokes, the relationship won’t get far.

And there are some things that, although quite small, can have a major impact on the success of a relationship. For instance, many people are surprised at how difficult it is to move in with their longtime partner. You love each other, and that’s the most important thing. Sure, you have your individual quirks and pet peeves, but those are minor issues…Right? But if you’re a neat freak and your partner’s a slob, you might be surprised at how quickly you get frustrated with and resentful of each other. Seemingly small differences like this can wear down a relationship—which is why, in many ways, opposites are not compatible.

But that’s no reason to dismiss your own polar opposite. Usually the traits that attract us to someone are not the same traits that determine our compatibility. Just remember, if you find yourself delving into something serious, it’s important to consider the differences that might affect your partnership down the road.