Les Binet and Sarah Carter get a little bit angry about some of the nonsense they hear around them… like the idea that marketing always needs to make sense

Many years ago, we worked on a tea brand. It had strong sales and had led the market for many years. It benefited from a very popular long-running ad campaign and was bolstered by very stable numbers of buyers, whose habits seemed ingrained. It was hard to see this situation changing much. They rarely do.

So when word got out that a tea competitor had a bizarre new product up its sleeve, we and the client were not unduly worried. Our brand came in square tea bags like the rest of the market. The competitor's new tea idea was round bags. This made no sense at all. The tea would taste just the same. We gave it a few months, at best. How wrong we were. People loved the new round bags. And our rival shot to brand leader within a year.

We were reminded of this story when we recently visited an exhibition celebrating the career of the fashion designer and retailer Paul Smith. Among his mantras for successful design was: 'Don't make sense'. He was right. The round tea bags made no logical 'sense' at all. But this didn't matter. People somehow liked the 'feel' of these new round bags. They seemed friendly, cosy, more tea-like. They even fitted more snugly into the bottom of a mug.

It seems to us that this little story illustrates one of the great lessons in marketing: things don't always need to make sense. Often the big differences come from small things with no logic or function.

In one famous psychological experiment, people had to select a loaf of bread. These were identical. Except one had a random alphabet letter stamped on it. It made no sense to choose that loaf over the others. But that's what people did. As Byron Sharp reminds us: it's often more important for brands to be distinctive than truly different, functionally.

These minor differences seem to work best when they give us a little emotional reward. We did some econometrics recently on a pet-food brand's online marketing effectiveness. The most successful activity wasn't the promotions or the product information. It was a funny little animated cat app that people could play with on their mobiles when they were bored. This didn't 'make sense'. But it had by far the highest RoI.

Similarly, it doesn't make 'sense' for Coke to sell cans with people's names on them. It didn't make much sense for Cadbury to sell chocolate with a gorilla. And it doesn't make sense for Innocent Smoothies to amuse people on its packaging. But when you do things that make people smile, they tend to buy your product.

There's a generosity of spirit about a lot of this stuff – the brand is giving us an emotional freebie. And behavioural economics shows that we get disproportionately excited about free things – especially stuff that we get here and now. This helps explain the success of 'instant win' promotions, and why UK supermarket Waitrose's new scheme offering a free coffee to its myWaitrose card customers has been such a storming success. People much prefer a free latte now to collecting points for reductions on future buys. Waitrose now apparently serves more coffees in the UK than anyone apart from McDonald's.

These little differences are just the kind of things that get trimmed by rational, cost-benefit marketing, because it's hard to say 'why' they work. Why names on cans? Why a funny cat app? Why free coffees? But there's hard economic evidence that they work very well. So, next time you're presented with a little idea that feels good but doesn't make sense, don't ask: 'Why?' Ask: 'Why not?'

Remember: often in marketing, it's sensible not to make sense.

This article originally appeared in the March 2014 issue of Admap. Click here for subscription information.