Which cookie would you rather eat?

If you're anything like the 626 people we asked you'll have plumped for the one on the left. An overwhelming 66% preferred it.

This cookie experiment was originally developed by Adam Ferrier of cummins&partners, who conducted it at Nudgestock with the same findings.

But why? The differences are minor. The cookie on the right is perfectly round whilst the other has a rough edge. Could it be that the small imperfections made the snack more appealing?

A series of academic studies suggests this is a widespread phenomenon. Eliot Aronson, from the University of California, was the first academic to investigate this bias, now known as the "pratfall effect".

Aronson recorded a colleague answering a series of quiz questions. The colleague, having been primed with the answers, answered 92% of them correctly. At the end of the quiz the colleague then pretended to spill a cup of coffee over himself.

The recording was played to a large sample of students, who were asked them 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. Overwhelmingly, the students found the clumsy contestant more likeable.

These findings have been repeated in a number of settings. Jo Sylvester, a psychologist at the University of Wales, for example, found that candidates who admitted past mistakes at job interviews were more appealing.

So why do these imperfections make products or people more attractive? And more importantly how can brands apply the learnings?

It might be that by admitting weaknesses brands seem more human or, in the case of the cookie, natural. In an age where many prefer the authentic to the mass produced this might boost appeal. Or could it work because everyone assumes that brands are fallible. If a brand is open about its flaws it can convince consumers that its weaknesses lie in inconsequential areas.

Claiming perfection leaves consumers fearing the worst and perceiving the brand as a braggart. This theory might explain the success of the low cost airlines. At launch they openly admitted that the trade-off for cheap prices was a compromised service: no reservations and a small luggage allowance. If they hadn't admitted as much, consumers may have assumed the cost-cutting had come at the expense of safety.

Counter-intuitively, the perfect brand strategy may be to admit imperfection.