diet Coke: It's possible that a major brand has nowhere to go, but down.

David Kiley

So, Coca-Cola has moved diet Coke to another agency in the hopes of reviving the flagging fortunes of diet Coke. Wieden & Kennedy is taking over for Draft/FCB. Why? Because Bor the first nine months of 2006, the brand's volume in grocery, drug chains, convenience and gas, and mass merchants excluding Wal-Mart fell 3%, according to Beverage Digest, despite ana increase in ad spending.

Here is a possibility to conside: That no amount of advertising creativity is going to reverse that trend, and that perhaps Coke should just manage diet Coke downward to maximize profit on a dwindling base of customers.

Cola drinkers have long been in decline. And we know why. Vitamin water, teas, fruity teas, Red Bull...the list goes on. People don't pass on diet Coke because Vitamin water, teas, fruity teas and Red Bull have a cooler image. They drink them because the taste or kick is more to their liking. For older boomers who grew up in diet Coke...we drink less and less cola, even diet cola, all the time.

I worked for the diet Coke agency a decade ago that came up with a decent enough tagline..."This is Refreshment." The tag was nothing, but it provided a new platform for a different kind of advertising that replaced "Just for the taste of it." The ads packed a lot of buzz---especially a memorable ad featuring a construction worker (named Lucky Vanous) taking off is shirt in front of a group of ogling secretaries. Another ad was set to music from The Band, and featured a woman in a dusty town obviously liberating herself from a no-good cowboy boyfriend. It was all pretty engaging stuff...telling little stories to associate with the brand. The public and media were really talking about it.

The idea in the campaign was people were choosing refreshment in different ways, but that diet Coke was part of the refreshment they were seeking, no matter whate else they were doing. The ads, especially the "Lucky ad," got a huge amount of bounce and buzz in the general media. But then Coke marketing czar Sergio Zyman up-ended the strategy after six months and reverted back to "Just for the taste..."

diet Coke has been declining ever since...in the U.S. anyway. Changing a campaign after six months was madness. Part of the reason these brands never get good traction again, I believe, is that churning sales and and marketing people at the clients don't believe in consistency any more. They are like ADD ferrets (to use a phrase from GM exec Paul Ballew) on crack. If you can't make up your mind about what this brand is supposed to be and stand for in the marktplace, how can consumers be expected to figure it out.

Some brands just hit a natural peak, and its downhill from there because tastes change. Coke can lard up diet Coke with flavors of lime, coffee, lemon or cherry if they like...but it's still a diet cola...and I just dont think diet colas are ever going to be on a growth curve again. If you are going to dispute that theory, then at least have the good sense to choose a brand platform and stick to it for more than a few quarters, and manage the brand as best you can for profitable decline.

Until Coke admits that and starts managing the brand profitably for what is probably diet Coke's inevitable continued decline from its previous peak, though, they'll just keep churning ad campaigns and agencies with little payoff. I suppose changing agencies again, though, gives the newest team installed to figure out the diet Coke problem some months of political cover until they are re-assigned to another brand or country. Then another crew will come in and repeat the process again. What business school teaches this anyway?