In the advertising surrounding Valentine's Day, we are bombarded with images of perfectly matched couples. You know the ones: the gorgeous and impeccably styled pairs that look great holding long-stemmed glasses of wine.

We might assume these duos only exist in movies and commercials, but everyone seems to know a real-life couple that appear perfectly in sync, share all the same interests and finish each other's sentences.

Dr. Blake Woodside, a professor in the psychiatry department at the University of Toronto, refers to such partners as "heavenly twins."

"They’re about five per cent of couples, but they’re held up as the ideal," he said.

Much more common, said Woodside, are complementary couples – partners who have their differences but, like interwoven fingers, manage to create a firm lock.

"That can be an extremely enduring arrangement, as long as the pieces fit reasonably well together," he said, adding that the search for perfection is a "terrible burden" and that there is no "magic formula" to finding love.

Tell that to the many people who believe you can take a calculated approach to romance, especially through online dating.

Amy Webb, CEO of U.S. digital strategy firm Webbmedia Group, recently published Data: A Love Story, a book that details how she hacked Cupid's algorithms.

The self-identified "professional disruptor" created a list of 72 different traits — some of which she called "top tier" variables — to pinpoint exactly what she wanted in a partner.

Then, with the help of spreadsheets, charts and a bit of math, Webb says she gamed Jewish dating site JDate to find her match.

"As long as you know exactly what you’re looking for, it’s no different from doing a search in a library or doing a search for shoes on Zappos," said Webb in a recent interview with social media news site Mashable.

"When you think about it, online dating is sort of the ultimate exercise in product marketing. Except that you are the product. So how can you leverage what you’ve got, how can you make sure you’re being seen by the most number of people?"

Love in the time of internet dating

This elaborate approach worked for Webb, whose husband, Brian, wrote the epilogue to her book, but not everyone would find it practical, or even palatable, to reverse-engineer one’s way to romance.

According to a comprehensive study released last year, online dating has become the second-most common way for people to meet (the first is meeting through mutual friends).

• Online dating may encourage shopping for mate

Researchers from five universities, including UCLA and the University of Rochester, collaborated on a comprehensive analysis of online dating. They argued that the "shopping mentality," represented in the extreme by Webb’s story, leads singles to become too focused on checking off a rigid set of criteria — like attractiveness or certain interests — or fixated on finding a "soulmate."

In the process, people may be missing out on good partners that are a less obvious fit.

"You’re much less likely to fire up the web browser and say, 'Let’s look for someone radically different,'" study co-author Eli J. Finkel, a professor of social psychology at Northwestern University, told CBC News.

He noted three ways in which online dating makes it more likely that singles will meet people similar to themselves.

For one, when singles search for potential matches, they tend to focus on and contact people with common interests. Secondly, when matchmaking algorithms are involved, similarities are typically preferred and differences digitally weeded out.

And third, more and more singles are limiting their search to niche dating sites — such as Stache Passions, which caters to mustachioed men and their admirers.

"If you have an absolute deal breaker, fine," said Finkel, offering the example of religious sites for those who want to date within their faith community.

"But there’s little evidence that by systematically ruling people out, you're improving the dating pool."

Similar does not mean complementary

Samantha Joel, a PhD student in the psychology department at the University of Toronto, studies how people make decisions about their romantic relationships — whether they're deciding who to pursue, who to hold on to or who to break up with.

Joel said the research in this area generally supports a "birds of a feather" motto rather than "opposites attract." But she adds there are important nuances to consider.

"On average, similarity is much more likely to help rather than hinder a relationship," Joel told CBC News. "But, the types of similarities that matter aren't necessarily the ones that stand out when you meet a couple."

Joel explained that less visible similarities, like common life goals, can be much more important than highly visible similarities, such as a difference in age or height.

She cautioned, however, that "similar" does not always mean "complementary."

"Some traits work better like a puzzle piece," Joel explained, offering the example of the career-oriented go-getter who pairs up with someone happy to go with the flow.

In non-abusive relationships, such contrast can be positive.

"Couples who seem different may have congruent goals," she said, adding that advice is always tricky in the abstract. "A couple can be very dissimilar and make it work."

Kathryn Guthrie of the Ontario Association of Marriage and Family Therapy agrees.

"Two peas in a pod may be very comfortable together — and after a while, they may be bored," said Guthrie, who has 17 years of experience counselling all kinds of couples.

"Opposites can attract, and then drive you crazy."

The important thing, she says, is that both partners feel valued, respected and understood. She also advises every couple, regardless of their arrangement, to work on communication, practice patience and know that every couple argues — but some argue effectively.

In that sense, so-called unlikely couples, heavenly twins and everyone in between can benefit from Guthrie's deceptively simple advice, which is to ask yourself a basic question. "Do I feel understood, and am I trying to understand my partner?"