Warwick Cairns explores the effectiveness – and limitations – of celebrity endorsement in advertising.

When Harry Met Sally. Even if you haven’t seen the movie, you probably know the scene. Billy Crystal and Meg Ryan play a couple in the throes of an on-off relationship. In the scene that’s now more famous than the film itself, they’re sitting at a table in New York’s crowded Katz’s Deli, when Ryan starts faking a long, loud and noisy orgasm. People stop with food halfway to their mouths. A bartender pauses mid-pour. Right at the climax, a waiter goes to the nearby table of a pair of middle-aged ladies to take their order, and gets the classic deadpan line, “I’ll have what she’s having”.

Smart advertisers have known for a very long time that when it comes to desire, when we see people living lives we’d really love to have, doing things we’d really love to do, what we want, what we really, really want, is a little bit of what they’re having. Doesn’t matter if the deli’s pastrami on rye doesn’t give you an actual orgasm. Doesn’t matter if you don’t look like Meg Ryan. Or Billy Crystal. By having what they’re having you’re just somehow making yourself a bit more like them. It’s why sports fans turn up at matches wearing perfect functional replicas of the kits worn by their heroes, rather than just wearing the team colours.

French philosopher René Girard called it the mimetic theory of desire. He said that rather than evaluating things on their merits, we all look to aspirational role models to see what they have and what they want, to help us work out what we ought to want.

Which takes us out of Katz’s Deli and into the nearby McDonald’s. Increasingly seen as big and boring, the brand was losing share amongst the young, multicultural audiences who were the drivers of the quick service restaurant category. With the accelerating pace of ethnic and demographic change in the US, this was becoming a real problem for them.

Desperately needing a way to make McDonald’s aspirational to a new generation, they came up with an insight that was both surprising and true. Most of the audience they wanted to reach could never afford to buy most of the things their icons had – except for one thing. Unless you really are Kanye West or Kim Kardashian you can’t buy a crystal-encrusted Ferrari, or an LA mansion. But you can buy their McDonald’s order. Because, believe it or not, these people do go to McD’s from time to time. Most Americans do. And they get the exact same flavour and quality as everyone else. To paraphrase Andy Warhol’s famous quote about Coke, no amount of money can buy you a better McDonald’s than the one the bum in the corner has.

So this is what McDonald’s did: they packaged up a set of “famous orders” and released them as limited-edition meal deals. Global pop sensation BTS, rapper Saweetie and Colombian singer J Balvin are three recent collaborations. People went crazy for them. There were queues outside some restaurants the night before the launch of the Travis Scott meal. People stole posters to sell on eBay. Sales went through the roof. People wanted a bit of what their icons were having.

All of which might lead you to conclude that instead of all this fancy strategy stuff, the only thing brands really need to do is to slap a famous face on their products, and then sit back and watch the profits roll in.

But it doesn’t always work out that way.

McDonald’s insight worked because it was both surprising and true. But most of the time, when celebrities endorse brands, it’s not exactly surprising and we very much suspect that it’s not entirely true. We often suspect that they’re only doing it for the money. Sometimes they don’t even bother to hide it. Like Helena Bonham Carter, chosen as the face of cosmetics brand Yardley, who said “I don’t know why they chose me. I don’t wear much make-up.” Or Charlize Theron, who took $3m from Swiss watchmaker Raymond Weil, and then turned up at a film festival wearing a watch by rival brand Christian Dior. Things like this are a lose-lose situation. They make the consumer feel a fool. They hit the brand’s sales. And while they may make the celebrity richer, their long-term reputation can suffer. Meanwhile, Bonham-Carter lost her contract, and Theron was sued.

Some celebrities do use the products they’re paid to – and talk about them too. But sometimes they say the wrong things. As LeBron James did with his new Samsung Galaxy Note III, tweeting to his 12 million followers that his phone had just rebooted and erased everything in it, and that it was “One of the sickest feelings I’ve ever had in my life!”

Then there’s what happens if you tie your corporate reputation too closely to an “inspirational” celebrity who then falls from grace. The bar for reputational meltdown used to be set quite high at one time. Like getting arrested for murder, as Nike ambassador Oscar Pistorius and Hertz frontman OJ Simpson both were. But in today’s volatile social media it’s much easier to get caught out doing or say the ‘wrong’ thing and go from icon to pariah overnight, as JK Rowling can testify.

The mimetic theory works – with caveats. “Having what she’s having” can be a powerfully effective motivator of desire for brands and products, if it’s used intelligently and well. But, to be effective, it has to be surprising, and it has to be true. Rather like a little-known fact about When Harry Met Sally: the actress director Rob Reiner cast as the lady envious of the orgasm-inducing meal was his own mother.