Sir John Hegarty says the advertising industry's creativity problem has gotten worse since he first warned about it nearly a decade ago – and data obsession is still to blame.

"If anything, it has gotten worse," Hegarty tells Marketing Week. "We're making a product that people increasingly dislike, and they dislike it because it's not very entertaining. It's repetitive, cliché, boring, all at a time when the ability to attract attention has never been more important."

The 82-year-old advertising legend, who headlines Marketing Week's Festival of Marketing on Wednesday 14 October, first told Marketing Week the better part of a decade ago that creativity was receding from the profession. He now points to studies showing consumers see advertising as something that has decreased in value and is an irritant rather than additive to their lives.

"We're disliked. Not valued. In a way it's tragic because one of the functions of a brand is to become a part of culture," he says.

Left-brain leadership

Hegarty blames agencies and brands staffed by "left brain thinkers" – people who understand a spreadsheet but "don't really get an idea". He recalls a lunch with Pixar founder John Lasseter, who told him a healthy creative industry needs creative people at the top of it.

"We've got all these people running large organisations that look at data and think data has the answer," says Hegarty. "Data doesn't have the answer. Data is knowledge. It's interesting, sure, but it doesn't imagine tomorrow. That's what marketing should be doing."

Critics will argue a data-rich culture has driven effectiveness up and wastage down. Hegarty counters with product launch failure rates: roughly 95% of new product launches fail, a figure he says has stayed fairly consistent over the last 20 years.

"And you go, but wait a minute, if you're so good and you've got more tools and data, why hasn't that improved? Why hasn't that got better?" he says.

The missing metric: taste

The one metric marketing has ignored, Hegarty believes, is taste. He points to the fashion industry, entirely dependent on taste and whether it captures what the public wants at any given time.

The motor industry offers a lesson too. Working with Audi in 1999 around the launch of the Audi TT, Hegarty arrived ready to talk about leading with technology, only to be told he had misunderstood the product.

"It was the look that was the leap – and they were absolutely right," he remembers.

Marketing has stopped accounting for those moments, he argues. "They've got the science and the data and everything else, but it looks like shit, they're not in any way imbued with that sense of the importance of how it looks and feels," he says. "And in a world which is oversupplied with everything, the decision-making process often comes down to that. Do I like the look of it? Do I feel it is great?"

Taste cannot be measured – perhaps that is the point. For Hegarty, if everyone has access to the same data, distinctiveness is the only way to stand out, and too many marketers avoid that question.

What's old is new again

On the trend of reviving past campaigns, Hegarty refuses to chastise marketers. "We've always had that with advertising. That eagerness of when do we stop that campaign and move on to something else. I always think we move on too quickly," he says.

He cites James Bond: a franchise built on one core idea for decades, repeating the same piece of music, yet constantly reinvented. "It's very hard to become a part of culture when you keep changing unnecessarily," he explains.

He holds up John Lewis as a cautionary tale. The retailer returned to 'Never Knowingly Undersold', "never knowing how stupid it was to stop doing it in the first place".

"Why did you change from that? It's a failure of imagination, a failure of understanding how brands are built, we have an industry of people who really don't know how it works," he says.

Brands need a manifesto

Hegarty also blames a new generation of digital-native marketers who avoid talking to people who "aren't going to buy their product" in the name of efficient, focused spend. This, he says, misunderstands how brands are built.

"A brand is made not just by the people who buy it, but by the people who know about it," he says. "And, I guarantee you, 90% of marketing people don't understand that."

His prescription: brands should think like movements. The great art movements, from the Dadaists to the Surrealists, had a manifesto of what they stood for. "Some of them were pretty daft but at least they had something," he jokes, urging every marketer to write a manifesto detailing what the brand believes in.

"I see lots of brands who just seem to have no purpose. They provide a need, but they don't create a want," he says. "How do I create want? That's based on taste, on ideas, on creativity and on all the things that brands should be employing – but they're not."

Sir John Hegarty appears as a keynote speaker at Marketing Week's Festival of Marketing on Wednesday 14 October.