Your main task this afternoon is to interview the last two candidates for the position of manager on your team. At the close of the second interview you realize both candidates have the same relevant experience, strong academic results and practical ideas to implement once they start. You’re wondering how you’ll ever choose between them. As the final candidate gets up to leave, he catches his foot awkwardly on the table leg, upending the dregs of his coffee over the new floor. He leaves ashen-faced.

Who do you think you’ll end up picking? If the Pratfall Effect is correct, it’ll be the clumsy candidate.

The bias was discovered in 1966 by Harvard University psychologist Elliot Aronson. Along with his colleagues, Ben Willerman and Joanne Floyd, he recorded an actor answering a series of quiz questions. In one strand of the experiment, the actor—armed with the right responses—answers 92% of the questions correctly. After the quiz, the actor then pretends to spill a cup of coffee over himself (a small blunder, or pratfall).

The recording was played to a large sample of students, who were then asked how likeable the contestant was. However, Aronson split the students into cells and played them different versions: one with the spillage included and one without. The students found the clumsy contestant more likeable. In Aronson’s words:

The pratfall made the contestant more appealing as it increases his approachability and makes him seem less austere, more human.

It’s not just clumsiness that increases appeal. My research partner Jenny Riddell and I investigated whether product flaws could boost appeal. We replicated an unpublished study by consumer psychologist Adam Ferrier by asking 626 nationally representative people which of two cookies they preferred. The biscuits were identical apart from one small difference: one had a rough edge; the other a perfectly smooth one.

The cookie with the rough edge was the overwhelming favorite: 66% preferred it. The small imperfection didn’t detract from its appeal, but boosted it.

Here’s how advertisers have applied this effect, and what we can learn from them.

1. Flaunt your flaws

The best application is to admit that your brand has a flaw.

Foolhardy?

Not if you consider how many of the leading ad campaigns have done so.

One of the earliest examples was the long-running American VW ad campaign by Doyle Dane Bernbach, which from 1959, gloried in the flaws of the Beetle. The looks of the car were gently mocked with one print ad featuring a photo of the lunar module and the headline, “It’s ugly but it gets you there.” Another referenced the size of the car with the line “Think Small.” And my favorite drew attention to the slow speed in the body copy: “A VW won’t go over 72 mph. (Even though the speedometer shows a wildly optimistic top speed of 90.)”

The trade magazine Ad Age ranked it the best ad of the 20th century. More importantly, it shifted a lot of cars. In 1963 VW sold 277,008 vehicles in the US—more than any other imported brand had ever sold.

Bill Bernbach’s agency repeated the honest approach with Avis. The tagline, written by Paula Green, emphasized the car rental’s relative unpopularity compared to Hertz: “When you’re only number two you try harder. Or else.” Within a year of the campaign launching, Avis made a profit of $1.2m—the first time they had broken even in a decade. The approach was so successful it ran for more than 50 years.

Then there’s Lowe’s campaign for Stella Artois, beginning in 1981, which revelled in its high price under the headline, “Reassuringly Expensive.” The award-winning campaign transformed Stella’s fortunes and ran for 26 years.

Guinness and AMV publicized the slowness of the pour with “Good things come to those who wait.” The National Dairy Council alluded to the high calorific content of cream cakes with “Naughty, but Nice.” (Incidentally, that tagline was coined by Salman Rushdie while working at Ogilvy & Mather.)

Admitting weakness is a tangible demonstration of honesty and, therefore, makes other claims more believable. Further to that, the best taglines harness the trade-off effect. We know from bitter experience that we don’t get anything for free in life. By admitting a weakness, a brand credibly establishes a related positive attribute.

Guinness may take longer to pour but boy, it’s worth it. Avis might not have the most sales but it’s desperate to keep you happy.

Everyone assumes that brands are fallible, so if a brand is open about its failings, it can persuade consumers that its weaknesses lie in inconsequential areas. This theory partly explains the success of budget airlines. At launch they openly admitted that the trade-off for cheap prices was compromised service: no seat reservations and a pitiful luggage allowance. If they hadn’t admitted as much, consumers may have assumed the cost-cutting had come at the expense of safety.

2. Make sure this tactic suits your brand

A twist in Aronson’s experiment suggests caution. He repeated the set-up but this time the actor feigned incompetence and answered only 30% of the questions correctly. Once again students rated his appeal. In this scenario the clumsy spillage made him less appealing. The Pratfall Effect has a multiplicative effect rather than a purely positive one. It makes strong brands stronger, but weak brands weaker.

The Pratfall Effect works particularly well when the competitors are braggards. And nowhere is hyperbole more prevalent than among estate agents. Roy Brooks carved out a profitable niche in the 1960s by selling houses in a brutally honest manner. Here’s a typical ad:

Wanted: Someone with taste, means and a stomach strong enough to buy this erstwhile house of ill-repute in Pimlico. It is untouched by the 20th century as far as conveniences for even the basic human decencies are concerned. Although it reeks of damp or worse, the plaster is coming off the walls and daylight peeps through a hole in the roof, it is still habitable judging by the bed of rags, fag ends and empty bottles in one corner. Plenty of scope for the socially aspiring to express their decorative taste and get their abode in The Glossy, and nothing to stop them putting Westminster on their notepaper. Comprises 10 rather unpleasant rooms with slimy back yard, 4,650 Freehold. Tarted up, these houses make 15,000.

In another ad he honestly appraised the rickety stairs in a house for sale:

A lightly-built member of our staff negotiated the basement stair, but our Mr Halstead went crashing through.

Nor were buyers spared:

WE HAVE A RATHER REPULSIVE OLD MAN who with his child-wife, are looking for an elegant town res. pref Belgravia…Price not important but must be realistic as he has, at least, his head screwed on the right way…

Brooks’ bravado paid off. His unique style earned untold levels of publicity: readers of the Sunday papers made a habit of seeking out his ads and he regularly appeared on TV chat shows. If you work in a category typified by overly positive descriptions, such as luxuries, cars or cosmetics, then this approach might be suitable.

It’s also worth considering the gender of your target audience. Kay Deaux, Professor of Psychology at New York City University, conducted an experiment in 1972 that showed that men are more swayed by the Pratfall Effect than women. If your brand targets men then admitting weaknesses should be an approach you seriously consider.

3. It’s not only ads

Finally, it’s not just a matter of tweaking the copy in your ads. It should affect how you deal with unflattering customer reviews. Many brands hide the negative reviews. However, a 2015 study, by Northwestern University’s Spiegel Research Centre, analyzed 111,460 product reviews across 22 categories and linked ratings to probability of purchasing. It found that likelihood of purchase didn’t peak with perfect scores but at 4.2-4.5 out of 5. There was only minor variation between categories—hair care reviews, for example, peaked in effectiveness at 4.2, while 4.5 was ideal for light bulbs.

Perfect ratings had less impact because they were seen as too good to be true. According to the authors:

Counter-intuitive as it may seem, negative reviews may have a positive impact because they help establish trust and authenticity. Consumers understand that a product can’t be all things to all people.

My favorite such example comes from Iain Banks’s 1984 debut novel, The Wasp Factory. Banks was thirty when he finally persuaded a publisher to release one of his works. The delay was not for want of trying. Over the previous 14 years he had written four novels, all of which had been rejected by publishers.

Despite struggling for so long to gain recognition, Banks broke with tradition and insisted that the novel included both positive and negative reviews within the blurb. Some of the reviews were caustic, such as the following from the Sunday Express:

A silly, gloatingly sadistic and grisly yarn of a family of Scots lunatics, one of whom tortures small creatures—a bit better written than most horror hokum but really just the literary equivalent of a video nasty.

The Times was even more damning:

As a piece of writing, The Wasp Factory soars to the level of mediocrity. Maybe the crassly explicit language, the obscenity of the plot were thought to strike an agreeably avant-garde note. Perhaps it’s all a joke meant to fool literary London into respect for rubbish.

Banks’s chutzpah paid off. His distinctive approach got him noticed and the sheer outrage of many critics meant its positioning as a powerfully moving book had credibility. The publicity helped create a bestseller, while positioning him as an independent thinker.

If it’s a successful approach, why is it rare?

I have listed half a dozen examples of the Pratfall Effect and there are a handful of others. But they stretch over a period of nearly 60 years, making them a minuscule proportion of the tens of thousands of ads that have run over that time.

Why?

The rarity is explained by the principal-agent problem, a theory first suggested by Stephen Ross, Professor of Finance at the MIT Sloan School of Management. He suggested that there is a divergence between the interest of the principal in a company, the shareholders, and the agent, the staff.

What is in the interest of the brand, the principal, is not in the interest of the marketing manager, the agent. If the campaign flops it might be the end of the brand manager’s career. Imagine explaining to your CEO as sales dive that the key message of your campaign was that the brand was expensive. Even referencing Aronson’s research won’t save you.

For those prepared to embrace a modicum of career risk then the best chance of growing your brand is to flaunt your flaws. The principal-agent problem ensures it will always be a distinctive approach. For those interested in safe career progression then you may want to consider another route, such as avoiding the winner’s curse. Luckily for you that’s what the next chapter is about.

This article has been adapted from The Choice Factory.