The jury is out on whether the latest sequel ad, T-Mobile's "singalong" filmed in Trafalgar Square and starring Pink, is as good as or better than its predecessor "dance".
So far, one week in, results are looking positive. The ad has already got three times the YouTube hits that "dance" did. But creatively, "singalong" lacks something of the spontaneous feel of its predecessor, probably because of the organised nature of the event.
The problem of how to follow a runaway success might be one that any agency would like to have. But recent follow-up ads - most notably Sony Bravia "paint" and Cadbury's Dairy Milk "trucks" - have not been a patch on their predecessors.
Phil Rumbol, the Cadbury marketing director for Britain and Ireland, says there was "a certain inevitability" that the sequel to "gorilla" would be disappointing because the first ad was so groundbreaking that expectations were very high.
The same problem rears its head in the music business, where "second album syndrome" is well-documented. Sequels often tend to flop because there is a tendency to revert to what was successful the first time around.
Neil Dawson, the global creative director for Philips at DDB, says: "You've got to recreate the situation the ad was created in, not the ad. That's incredibly difficult when suddenly everyone wants a piece of it. There's more involvement. The only way you're going to get cut-through work and continue to do the spectacular is to astound the client in a different way."
The first rule of thumb, the experts say, should be to evolve the idea, retain some elements of the first ad but keep consistency of thought. Easier said than done, but, done well, this should keep things fresh and deliver something that moves the last ad forward, rather than going over the same old ground in a paler version.
Timing can also be an issue. With a sequel, creatives are often asked to recreate the magic, but to a much tighter timescale and generally from scratch.
The same problem, again, occurs in the music business. Shabs Jobanputra, the president of Virgin Records UK, says: "If it has taken years for an artist to make an album and wait to be signed, suddenly the masterpiece is out, but they've got to replicate it in 18 months which is extremely difficult."
Dylan Williams, the head of strategy at Mother, says that the move from one-off ad to sustained brand- building is the key challenge to creating a successful follow-up.
"In communications, you avoid sequel syndrome by not becoming a schizophrenic or flaky brand defined by the transitory tastes of consumers," he says. "I think looking at the wider world of entertainment and popular culture, the great brands have been the ones that are consistent over time, but manifest in fresh ways, such as Madonna or Goldfrapp."
Of course, second ad syndrome isn't an epidemic and creatives often point to Guinness' "swimblack" and "surfer" or Honda's "cog" and "grrr" as campaigns that started off brilliantly and continued to get better and better.
On those occasions, success was down to the brilliance of the people involved, who took risks to evolve strong ideas, Paul Silburn, Saatchi & Saatchi's joint executive creative director, says. However, he also believes that a situation as complicated and convoluted as this might all just come down to something as simple as a "combination of luck and judgment".
- Got a view? E-mail us at firstname.lastname@example.org
CLIENT - Lysa Hardy, head of brand and communications, T-Mobile
"There were two things we took into this second ad. The first one was to not recreate 'dance'. We wanted to do something that built on it, but was different. The second thing was to take the insight and the reaction to 'dance' and use it to base the idea on.
"I think there is a tendency to revert to what you did before because it worked.
"When we did 'dance', we'd never done anything like it before so we could take risks and be bold, but now the bar has moved and the expectation is there. The second time around, all of us thought: 'Crikey, we've got to get this right.'"
PLANNER - Dylan Williams, head of strategy, Mother
"Because of citizen journalism, the ability to become famous happens much more rapidly than at any time in history. If you do something good, everyone will know about it instantly through a degree of hysteria not previously seen. By the same token, you are more quickly disposed of and forgotten.
"In a way, that pressure creates a temptation to replicate the initial source of success, but the smart players recognise that you'll never be as successful the second time around because of the process of diminishing returns."
CLIENT - Phil Rumbol, marketing director, Britain and Ireland, Cadbury
"There are two things. One is understanding what made the first one successful and using that to guide the development of the follow-up. The second is to recreate the conditions that led to the first ad, by which I mean the atmosphere within the client and agency team.
"I think you need to watch out that you don't over-think things. Sometimes in working out how the first one worked, you constrict the thinking of the next one.
"Often great ads come out of a particular moment and a certain spontaneity. When you try to do that again, it changes the dynamics because you're asking different questions."
CREATIVE - Ben Walker, creative director, Wieden & Kennedy
"The answer is to work a lot harder. When 'cog' came out, it set a standard and anything below that wasn't good enough. People had to work harder to get the same result.
"There is more pressure, there's no doubt about that. Creatives will get a brief and think harder and spend more time on the weekend working on it, as they know what they have got to beat.
"We were lucky with Honda, it has a great history. It's not about us being clever, it's about the brand being good enough to tell a million stories."