Are lovers at first sight truly meant to be? That depends on how much they're willing to work to maintain passion once the smoke clears from Cupid's initial offensive.

A study of 137 couples found no difference in commitment, intimacy, or relationship quality between those who fell in love at first sight and those who were friends first. The friends-first partners had more similar personalities, and similarity creates more long-term harmony—opposites sometimes attract but less frequently adhere. But the Romeos and Juliets had an edge: more passion—even after an average relationship length of 25 years.

Researcher Pieternel Dijkstra of the University of Groningen notes that the subject pool was not necessarily representative: "I suspect that a lot of people who fell in love at first sight may already have divorced." She says initial infatuation is driven largely by lust—a beast rumored to be ephemeral. But that's not a death sentence for instant paramours committed to fueling the flames. Just look at the success stories who were in the study. There was one compatibility hurdle that even these dedicated romantics could not overcome, though: Passion couldn't compensate for differences in conscientiousness, a total drag on relationship quality.

Was it love at first sight for Dijkstra and her husband, study co-author Dick Barelds? "When I first saw him, I didn't feel sexually attracted to him, but I looked in his eyes and thought, well I think I will have some type of relationship with this person," she says. They were friends for six months and have now been together, married, for years. "I don't know if I can qualify this as love at first sight, but there was something at that first moment."