Relationship psychologist Esther Perel says there's a simple reason happy people cheat.

Being cheated on is an experience that feels intensely personal, but relationship psychologist Esther Perel says sometimes it has very little to do with the person who’s been betrayed.

In her latest book, The State of Affairs, Esther explains while people often cheat because of marital dysfunction, sometimes it can happen even when there’s no problem with the relationship at all.

So why, if someone is well-balanced, mature, caring and totally invested in their relationship, would they cheat on their partner?

“Straying isn’t necessarily a symptom of a relationship gone awry,” Esther tells Mia Freedman during an interview for No Filter.

“It’s the quest for lost parts of one’s self, it’s the quest for a sense of aliveness, for vitality.  It’s a quest to reconnect with the unlived lives.”

Listen:  Esther Perel tells Mia why it’s not only unhappy people who stray.

In these situations, cheating isn’t about compensating for something that’s missing in a partnership or setting up an exit, it’s about self-discovery. For these people, infidelity is less likely to be a symptom of a problem and more likely to be about growth, exploration and transformation.

To someone who’s just been cheated on, the excuse “I’m sorry, I was just trying to find myself” might be cold comfort, but Esther says when people seek the gaze of someone who isn’t their partner, it’s not always because they’re looking for another lover. It’s often because they’re looking for another version of themselves.

The problem is that when couples try to search for meaning they often experience the “streetlight effect” which means they oversimplify the problem to make it easier to solve.

“Human beings have a tendency to look for things in the places where it’s easiest to search for them rather than in the places where the truth is more likely to be found,” Esther says.

To hear the full episode of No Filter, listen here:

For some couples, focusing on the familiar territory of their relationship and blaming it for causing the infidelity is easier than delving into the complexities of a partner’s existential crisis and trying to understand it.

“Affairs are about hurt and betrayal and deception but they’re also about longing and loss and self-seeking,” says Esther.

Sometimes, those feelings are enough to make intensely faithful people risk everything and cross a line they never thought they’d cross.