Last week, we found ourselves having breakfast with a professor, no less. Over the scrambled eggs, we talked about the future of marketing. Of course, he said, brands need to move away from mass marketing to having more direct, personal relationships with their buyers.

Grrr… This kind of talk is everywhere these days. Words like ‘love’, ‘passion’ and ‘loyalty’ litter social media briefs and brand objectives. It's not enough for people to buy our products – we want ‘relationships’ with them.

A lot of this talk is metaphorical, but many people seem to take the relationship analogy literally. That's not just nonsense – it's dangerous nonsense. Think about brand relationships from the consumer perspective. It's a myth to believe we can take words like love and passion from our human relationships and blithely apply them to the brands we use every day. Real human relationships, even quite shallow ones, take a lot of time, effort and brain power to build and maintain. Some scientists believe the main reason we developed such big brains was to manage our relationships. But there seems to be a cognitive limit to the number of relationships we can handle. Beyond about 150 relationships (Dunbar's Number) our poor brains just can't cope any more.

That doesn't leave much headspace for brands. As the enlightened CMO of Mars said recently: “Most of us go through life finding it hard enough to have good relationships with the real people in our life, let alone all the brands we buy.”

And think what Dunbar's Number means for CRM. If you want to have a real relationship with your customers, you're going to have to assign one member of staff for every 150 customers. The numbers just don't make sense. And don't think you can fake a relationship with clever software. Millions of years of evolution have given us exquisitely sensitive social radar. Experiments suggest that even very young babies can distinguish between real and fake social interactions.

Contrary to marketing's ‘relationship’ desires, most of us require a brand to do little more than make our lives a bit easier, and then to get out of the way. Very few people want a real, human relationship with a brand. When they do, they're usually seen as immature (teenagers obsessing over pop stars) or slightly weird (people with Harley Davidson tattoos).

It's true that many brands have a few people who feel very strongly about them, and we should certainly make the most of their ‘passion’ (for example, by mobilising them to submit new product ideas, to blog positively about you, or to come up with communication ideas). But these brand ‘lovers’ will always be the exception, and rarely contribute much to the bottom line, even for cult brands.

Isn't this relationship myth just a bit of harmless fantasy? The danger is that our desire to create strong brand relationships distorts what smart marketing is really all about. Research shows that brands become big and profitable by building weak relationships with lots of people. We know that when budgets are diverted from this penetration building task to build deeper relationships with fewer customers, profitability suffers. It is just not economically viable to have deep personal relationships with all your cat food buyers.

It is often assumed that the weakness of these many ties represents a failure on marketing's part. In fact, this is just what people want. They don't want brands to be their friends. People love their cats, not your cat food brand.

Of course, there are areas of marketing where strong personal relationships do play a crucial role. It makes sense to spend time and effort building close bonds with important suppliers, distributors, designers, regulators, journalists and other opinion-leaders. But the main job of consumer marketing is not to build a few strong ties, but lots of weak ones.

Brands should aim to be more like Jeeves-type servants than friends or lovers. By and large, we like our brands to be attentive, charming and helpful when required, but otherwise to stay out of our way. Then we can get on with the relationships that really do matter to us – the ones we have with each other.