Iain Banks was a precocious child: by 14 he had written an unpublished novel.

Unfortunately, his early promise petered out. By his late twenties, Banks had written another three novels but all of them were rejected by the book industry. Desperate for success, he switched genres from his favoured science fiction to more mainstream fare. His decision paid off. Macmillan, one of the most respected publishing houses, offered him a contract.

The critical reaction to the preview copies was mixed. Some hailed the book as brilliant, but others were less enamoured. The Sunday Express declared it better “than most horror hokum but really just the literary equivalent of a video nasty.” The Times was more succinct  – “Rubbish.”

Rather than ignoring this criticism, Iain broke with tradition and insisted that the novel’s cover included both positive and negative reviews. Macmillan were aghast, but Iain was adamant. The negative reviews stayed. Banks thought the success of the book, The Wasp Factory, proved him right. In an interview, nearly thirty years later, he claimed that fans still stop him in the street to say it was his bold decision that first piqued their interest.

But was Banks right? Did the negative reviews contribute to his success?

The power of a pratfall

The psychological evidence supports Banks. Elliot Aronson, from Harvard University, has shown that people who exhibit their flaws become more appealing.

In 1966 Aronson recorded an actor answering a series of quiz questions. 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 much they liked the contestant.

However, Aronson split the students into groups and played them different versions: one with the spillage included and one without. The students found the clumsy contestant more likeable. Aronson termed the idea that people who exhibit a flaw become more appealing the “pratfall effect.”

It’s an insight that has been harnessed by some of the world’s leading brands, from VW admitting the Beetle was ugly to Guinness admitting they were slow.

Why is the “pratfall effect” so persuasive?

There are four reasons why so many iconic campaigns admit a flaw.

First, people are sceptical about advertisers’ claims. At best, they assume advertisers are partial with the truth, at worst they think advertisers lie. Admitting a weakness counteracts this scepticism as it’s a tangible demonstration of honesty, which makes other claims more believable.

Second, people know that no brand is perfect; that there are always trade-offs. Therefore, if a brand fails to admit a weakness, it leaves it to the shoppers’ imagination where those flaws lie. The danger is that people assume the worst.

Rory Sutherland suggests the canny use of the “pratfall effect” explains the success of budget airlines. At launch they openly admit that the trade-off for low prices is a compromised service: no reservations and a small luggage allowance. If they hadn’t admitted as much, travellers may have assumed the cost-cutting came at the expense of safety and they would never have stepped on board.

Third, the wisest brands don’t choose a weakness willy-nilly, instead they select one with a mirror strength. 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.

The final strength is that despite the volume of evidence supporting the pratfall effect, it is rarely used. In the last few years only a handful of brands (like the ad below for Snowbird ski resort) have harnessed the bias.

The body copy reads: Too advanced. I’d heard Snowbird is a tough mountain, but this is ridiculous. It felt like every trail was a steep chute or littered with tree wells. How is anyone supposed to ride in that? Not fun!

The rarity is explained by the principal-agent problem – the idea that there is a divergence between the interest of the principal, that is the brand or the shareholders, and the agent, the staff, or in our case the marketer.

The principal is interested in long-term sustainable profits, whereas the agent is also interested in their safe career progression. The pratfall effect doesn’t appeal to the agent because if the campaign bombs, it might derail their career. Imagine explaining to your CEO as sales dive that the key message of your campaign was that your car was ugly.

The selfish motivations of the agent ensure the pratfall effect will always be a distinctive approach and if there’s one thing we know about advertising it’s that what is distinctive, is memorable.

Paradoxically, the perfect brand strategy is to admit an imperfection.

Richard Shotton is the author of The Choice Factory and Manning Gottlieb OMD’s deputy head of evidence.