People have been trying to crack the relationship mantra for ages now and figure out what makes some couples last longer than others? Here’s what science has to say about the elusive "spark" that drives a long-lasting relationship.

The first factor that comes to mind is the “like attracts like” notion. But one’s preferences have a relatively small role to play in sustaining a relationship.

“Yes, it is true that people are more likely to experience chemistry with someone who is similar to them in certain ways,” Prof Harry Reis at the University of Rochester, New York, said, as per The Guardian. “But if I brought you in a room with 20 people who are similar to you in various ways, the odds that you’re going to have chemistry with more than one of them are not very good.”

However, extreme differences do play a role. “It’s not likely that you would have chemistry with somebody who is very dissimilar to you,” Reis added.

Even effects of factors like shared interests are “so tiny,” Prof Paul Eastwick at the University of California, Davis, said, according to the outlet.

Reis is also skeptical about the chances of dating app algorithms correctly predicting the right match, and added, “the evidence that they have is very, very low-quality work.”

According to Reis, these apps can at most separate people with the most extreme differences in personality and interest, but the rest is up to chance.

According to psychological research, it is the flow of the conversation and people’s nonverbal cues that are the deciding factors. “It’s whether the other person is smiling at the right moments, whether they’re really listening and showing that they understand what you’re saying,” Reis said.

To sum it up, Eastwick said, “No algorithm is going to be able to tell us that’s going to happen ahead of time.”

Another idea that many people place their faith in is the “attachment styles.” These are dictated by one’s childhood experiences with their caregivers. Self-explanatory, the attachment styles are “secure,” “avoidant” or “anxious.”

While the styles may have some influence, researchers warn against reading too much into them. Prof Pascal Vrtička, a social scientist at the University of Essex, pointed out our attachment styles are dynamic, and can change with the right partner. For instance, someone might change from anxious to secure with the right person. “It might take some time to lose some of your insecurity, but it is possible.”

Similarly, the concept of “love languages”--which is a person’s way of showing affection and appreciation for their partner--can affect a couple’s initial compatibility, but it can be changed over time.

All in all, science shows that love is unpredictable. There is no one-size-fits-all approach that can decide whether a relationship will last long or not. So go out there and be ready to be surprised.