In these types of stories, rejection uncovered a hidden flaw, one that led people to question or change their own views of themselves—and, often, they portrayed their personalities as toxic, with negative qualities likely to contaminate other relationships. One study participant wrote: “I learned that I have a part of my personality that sabotages my happiness.” Another confessed: “I just feel hurt and rejected. I try to tell myself that it wasn’t my fault and that it was that person’s loss but I can’t help but feel inadequate.”

Many of these stories were similar to the ones I’d heard from friends after their own breakups. The refrains were familiar: “Why wasn’t I good enough?” or “Is there something wrong with me?” When people see ex-partners in new relationships, they often ask themselves: “What does she or he have that I don’t?”

After a breakup, it can be healthy for people to reflect on what they’ve learned from the past relationship and what they want to improve in the next one. A healthy behavior can become an unhealthy one, though, when people take it too far and begin to question their own basic worth.

But the loss of a partner can make it easy to fall into the self-deprecation trap. Research by the psychologist Arthur Aron and his colleagues shows that when people are in close relationships, their self becomes intertwined with their partner’s self. In other words, we begin to think of a romantic partner as a part of ourselves—confusing our traits with their traits, our memories with their memories, and our identity with their identity. In a measure designed to capture the closeness of a relationship, Aron’s team ask people to consider themselves as one circle, their partner as another, and indicate the extent to which the two overlap.

To an extent, this overlap of the two selves can be a very positive part of relationships. As people get to know a new romantic partner, they often go through a rapid period where they immerse themselves in the interests and identities of their partner, adopting new perspectives and expanding their worldview. One of the greatest pleasures of being in a relationship is that it can broaden a person’s sense of self by exposing them to things outside of their usual routines.

But this also means that when a relationship ends, the loss of a romantic partner can, to some extent, cause the loss of the self. In one study, after reflecting on a breakup, people used fewer unique words to describe themselves when writing a short self-description. And the more people felt themselves grow during a relationship, the more likely they were to experience a blow to their self-image after the breakup.

In our research, people reported the most prolonged distress after a romantic rejection when it caused their self-image to change for the worse. People who agreed that the rejection made them question who they really were also reported more often that they were still upset when they thought about the person who had rejected them. Pain lingered from rejections that had occurred even years before. Writing about what they took away from the rejection, one study participant said: “Lots of emotional pain. Sometimes it keeps me awake at night … It’s been 10 years and the pain hasn’t gone away.” If rejection seems to reveal a new, negative truth about a person, it becomes a heavier, more painful burden.