KEY POINTS:
So it's not the pressure of the credit crunch; it's not halitosis, infidelity or the repeated failure to load the dishwasher that is going to do for your relationship. It's watching Notting Hill.
The latest research from the wonderfully named Family and Personal Relationships Laboratory at Heriot-Watt
University in Edinburgh suggests that romantic comedies such as You've Got Mail and Runaway Bride give people "unrealistic expectations" of relationships. It claims that fans of such films fail to communicate with their partners.
"Marriage counsellors often see couples who believe that sex should always be perfect, and if someone is meant to be with you then they will know what you want without you needing to communicate it," explains Dr Bjarne Holmes, who conducted the research. "While most of us know that the idea of a perfect relationship is unrealistic, some are more influenced by media portrayals than we realise."
The study observes that 100 student volunteers watching Serendipity, a rom-com about fate and destiny, were more likely afterwards "to believe in fate and destiny". The other 100 were given a David Lynch drama to watch.
Having written six novels that fall into the much-maligned category of "romantic fiction", I have a fairly good toehold on the line between story and reality. Watching ET didn't make me believe my bike could fly (okay, it might have done, but I was little), nor do I expect to give up on my husband of a decade - whose most recent romantic declaration was "I did think about buying you some flowers" - because he's not George Clooney.
In fact, Dr Holmes and his colleagues have failed to grasp the most common reason for watching or reading romance: escapism.
I recently received an email from someone who had decided to stop reading my latest book halfway through, even though she had been enjoying it. "I don't want complicated, messy relationships," she said. "I get enough of that in real life."
Indeed. Romantic comedy is a reliably successful film genre because the audience knows what it wants and the film-makers know how to provide it. It does not require computer generated imagery, explosions or exotic locations, just the answer to a never-ending preoccupation: how do we find love and how do we keep it?
The key to a great love story is the tension between what we want and what we are allowed. The true classics are driven by obstacles; what the award-winning writer Jeffrey Eugenides calls "the fly in the ointment".
We want to see people suffer, but to know they will be okay - a principle that dates back to the Stone Age, when oral storytelling was a way of reaffirming the idea that others had survived the same trials we were having to endure.
But in a world where couples hook up at the click of a button, divorce carries little stigma and adultery is common, what genuine obstacles remain? Would Brief Encounter have anything like the same resonance if Celia Johnson and Trevor Howard had engaged in a quickie on the train?
Matt Dunn, one of the few men to be shortlisted for the Romantic Novel Award for The Ex-Boyfriend's Handbook, says that a rom-com has to be contrived to satisfy.
"The maxim of romantic comedy film-writing is that the love story is over when the boy and girl kiss. It's the keeping them apart that's the most important thing," he says. Often, he says, the resolution we think we want weakens the dramatic pull: think Ross and Rachel from Friends, or Daphne and Niles from Frasier. Their love for one another went unrequited for years, but it kept us glued to the TV - until they finally got together, when we all rather lost interest.
Romantic comedy is often better than drama at reflecting real relationships: witness the painful bickering and point-scoring of Jennifer Aniston and Vince Vaughn in The Break-Up.
Bridget Jones was a success not just because of the fairy-tale conclusion but because a million single women saw a reflection of the tragicomedy of their own lives, big knickers, chardonnay and all.
And what are the films of Woody Allen about if not our inability to communicate what we really want?
British romantic comedy can be better - think of Gavin and Stacey, or the realistic courtship of Tim and Dawn in The Office.
TV series Cold Feet managed to mix the great romantic gesture (holding a rose with your bottom, anyone?) with the grit of everyday relationships.
The Heriot-Watt study concludes, rather pompously, that "depictions of relationships seemed contradictory and potentially confusing". "Characters often made great efforts with romantic gestures [but] were also shown... to neglect their relationships, deceive their partners, fight, argue and in some cases be unfaithful."
Exactly. What we really want from our love stories is contradictory - never more so than when it involves romance. We want characters we can identify with, but also a tale that lifts us from the mundaneness of our own experience. We want to see our lives reflected but also to be taken away from them.
Rom-coms can also be instructive. As author Kate Harrison suggests: "They can provide a great example for the men in your life to follow when they're looking for a romantic gesture."
But then, I suppose it's easier for the researchers to say that women are wrong for expecting some romance in their lives than for men to do something about providing it. I wonder how many roses Dr Holmes has grasped between his teeth lately?
Jojo Moyes is a former winner of the Romantic Novelists' Association Book of the Year award. Her latest novel, Night Music is published in Britain by Hodder & Stoughton.