Les Binet and Sarah Carter get a little bit angry about some of the nonsense they hear around them… like the mistaken belief in the relevance of 'relevance'.

Many years ago, we worked on Dulux. At that time, Dulux ads always featured a shaggy Old English Sheepdog. The dog would appear as a branding device alongside the packshot or during the ads, typically padding through beautiful newly-painted sitting rooms. Back then, Dulux made so many ads that they tested them using a proprietory pre-test. One standard question was: 'Why do you think there is a dog in this ad?'

We always felt rather sorry for the hapless respondents. What exactly were they meant to reply? There wasn't really any good answer (other than 'because there always has been a dog in Dulux ads), because there wasn't any good reason for the dog to be there. The story goes that once on a Dulux ad shoot, an Old English Sheepdog belonging to a crew member wandered onto the set. It looked good, so it was kept in. The rest was history.

Which brings us to this month's topic. Many of us were raised on a mantra that ads needed to be distinctive and relevant. But how important is relevance? The many successful, but 'irrelevant', advertising campaign ideas around today (from Russian meerkats to roller-skating babies) make us wonder if perhaps we overestimate the relevance of relevance?

Being 'relevant' may mean sacrificing perhaps more important qualities in an ad. Ads need to be interesting, because people have busy lives which don't revolve round brands. Paint isn't especially interesting, but dogs are. Ads need to be emotional, because that's what sells best, especially over the long term. Paint is not particularly emotive, but dogs are. Ads need to be branded on some level, and that's hard if they're not distinctive. If Dulux's ad had just focussed on the paint, it would have looked like any other paint ad, but the dog made it distinctive.

So, by making Dulux ads more interesting, emotive and distinctive, the dog made them more memorable. This is a general phenomenon. Experiments have shown that it is easier to remember messages when they're accompanied by completely unrelated, 'irrelevant' video footage. All this helps explain why some of today's most effective ads are based on 'irrelevant' ideas.

Over time, of course, what seems irrelevant at first can become relevant: eventually the shaggy dog in the ad (and in fact the entire breed) became instantly recognisable as The Dulux Dog.

But does that mean we can put anything in our ads? Not quite. We believe that the things we put in our ads do need to be relevant, in two much deeper senses.

Firstly, they need to be relevant to people's lives. As Bill Bernbach said: "A communicator must be concerned with the unchanging man – what compulsions drive him, what instincts dominate his every action." Paint is pretty peripheral to most people's lives most of the time, but pet dogs have deep associations with hearth, home and family – themes that are universal and unchanging (and not unrelated to paint).

Secondly, when you tap into these universal motivations, you tend to generate big emotions, which as we've seen can be very helpful. But it's important that we generate the right emotions for our brands. We need 'emotional relevance'.

For example, think of the ads Citroën once ran featuring supermodel Claudia Schiffer taking her clothes off. They generated either lust or anger, depending on your point of view, but neither emotion was relevant to choosing a car. Now contrast that with the recent Volkswagen ad, where the Dad gives a Polo to his daughter as she leaves home. That generated protective feelings that have always been part of Polo's positioning.

And therein lies the correct answer to that Dulux pre-test question: 'the dog is in the ad because he's a relevant irrelevance'.

This article originally appeared in the March 2013 issue of Admap. Click here for subscription information.