Which dating match will be more successful? Someone who is similar to you or different?
"Opposites do attract," says Dr. Neil Clark Warren, an expert of sorts in dating. "There's something fascinating about finding someone who likes you who is very different from you."
But in an interview with CNBC's "On The Money," the founder and CEO of the eHarmony online dating site warns that, over time, "opposites attract, and then they attack."
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After 35 years of counseling married couples, Warren says he's learned that "if the right person doesn't marry the right person, you've got real problems ahead. It's tough to bend people after they first get married."
Warren is a clinical psychologist and has written eight books on love and marriage. Fifteen years ago, he launched eHarmony, the site that helped pioneer the electronic dating era. The privately held company claims that 600,000 married couples have met on the site, which—if accurate—accounts for nearly 4 percent of all U.S. marriages.
The dating service business is a $2.4 billion industry, according to market research firm IBISWorld, while eHarmony has a nearly 14 percent market share among online dating sites. The leader in the category with a 21.8 percent share of the market is IAC/InterActiveCorp, which runs dating sites such as match.com, OKCupid and Tinder.
The eHarmony site charges up to $60 a month and requires users to fill out a lengthy questionnaire. Warren says: "We ask every question we can think to ask ... and we match them so carefully on 29 dimensions. We call it broad-based compatibility and it's what you have to have."
When asked what the most important characteristic is in successful relationships, Warren tells CNBC that "Intelligence is really important" when it comes to matching people for marriage.
The dating guru added that, "We have to ask the questions that get at intelligence so we can pair people up so they won't find themselves feeling hurt because the other person is saying things they don't understand."