It's not so much about actively resisting temptation as it is about not even perceiving it. deveion acker/Flickr While researching a story on signs that your relationship is failing, I came across one sign that seemed glaringly obvious — but that I'd never given much thought to before.

A study published in 1987 by Jeffry Simpson, then at Texas A&M University, found that people were more likely to break up with their partner if they felt as if they could find someone else just as good — or better — to date.

In other words, it's not necessarily about whether you've been actively flirting or intimate with someone else. In fact, there doesn't even have to be a specific someone else. Just the notion that you could find a replacement partner can portend the end of the relationship.

For the study, Simpson was interested in the factors that predict both breakups in nonmarital relationships and emotional distress following a breakup. He recruited about 200 undergrads who were in relationships, but not engaged or married, to fill out questionnaires about their relationships.

A few questions focused on what Simpson calls "alternative partners." Specifically, participants were asked to identify one person who was the best realistic alternative to their partner. Then they compared that person to their partner on different characteristics.

Next, participants were asked to imagine the best possible alternative dating partner they could realistically find. They compared the imaginary person to their partner on the same characteristics.

Finally, participants indicated how easily they could find someone to replace their partner, responding to statements like, "I would have little trouble finding someone who could serve as an adequate replacement for my current dating partner."

About three months later, participants were asked whether they were still dating their partners.

Results showed that participants were less likely to have gone through a breakup if they had a less desirable best actual or imagined alternative partner and if they thought they would have a harder time finding a replacement partner.

Other research suggests that people who pay more attention to attractive members of the opposite sex are also more likely to break up with their partners.

Of course, it's hard to say exactly why this happens. It could be that participants who are dissatisfied with the relationship give more consideration to alternative partners — or it could be the other way around, that participants who think they have solid alternatives are more disappointed in their relationships.

The not-very-romantic takeaway here seems to be that being in a successful relationship means having a restricted field of vision, in the sense that all the other fish in the sea seem less shiny and farther away than they did when you were single.

Bottom line: It may not be so much about actively resisting temptation as it is about not even perceiving it.