As Jimmy Greaves once famously remarked - and as Masterfoods is no doubt about to discover - football is a funny old game. It can also be unpredictable and cruel.
Of course, Wayne Rooney may blast the ball past the Brazilian goalkeeper in the last minute of injury time to win the World Cup for England. Then again, maybe he won't.
And by rebranding the Mars Bar as Believe for the duration of the tournament, Masterfoods may either reap the rewards for perfectly capturing the English collective mood or face the backlash of a crushing disappointment.
Masterfoods has decided the risk is worth taking. It is putting £3.7 million behind the initiative, which will embrace television, national press, outdoor and PR activity. There will also be a website, as well as promotional links with The Sun and talkSPORT.
Curiously, though, Masterfoods seems to have succumbed to pre-tournament nerves. Jonathan Rodd, the company's UK bars marketing controller, will say only the campaign "aims to harness the power of positive thinking among fans during the run-up to the World Cup", while Abbott Mead Vickers BBDO, the agency spearheading the initiative, is forbidden to discuss it with Campaign.
According to industry sources, Masterfoods, which is not an official World Cup sponsor, does not want to find itself accused of ambush marketing.
Fifa has instructed its lawyers to keep a close watch for any trademark infringements - they have already pursued about 1,200 cases in more than 60 countries around the world.
What is certain is that there will be a TV campaign featuring a fictional character called Bill Lever (geddit?) who was born at the moment Geoff Hurst scored England's winner in 1966 and is committed to getting everybody revved up for a repeat.
The ad takes in episodes from the England superfan's life and climaxes with himself and hundreds of other supporters celebrating the inevitable triumph.
So, how much of a gamble is it? After all, the Mars Bar name has never changed in the UK since its launch 86 years ago.
There is a widespread belief that you tinker with your name or your logo at your peril. Two years ago, McDonald's temporarily dropped its Golden Arches, replacing them with a question mark in the same typeface and the tagline: "McDonald's. But not as you know it."
The intention was to convince UK consumers it was changing. But the initiative, through Leo Burnett, was criticised for failing to get rid of negative perceptions.
Tim Broadbent is the former chief strategic officer of Bates Group Europe, a long-time Mars roster network, and now chairs Brandcon, a branding and evaluation consultancy. He believes the risk for Masterfoods is minimal, however, and the Mars Bar brand will benefit from the free PR mileage the initiative will generate.
"A lot depends on how England perform and we seem to have our best chance in years," he says. "If 'believe' is a disaster, Masterfoods can quietly forget about it. If it is successful, it will be seen as a brilliant tactic."
Steve Richards, the global chief operating officer of the brand consultancy Wolff Olins, worked on Mars when he was the managing director of Grey London. He also thinks the idea can work. "I think it's a really innovative idea, which encapsulates the hopes that everybody has," he comments. "There's no design issue because the product's wrapping is in keeping with the look created for it. Also, knowing Mars as I do, I am sure this tactic will be repeated if it works."
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CLIENT - Chris Moss, European chairman, The Number group of companies
"Of course there's a risk in what Masterfoods is doing. But there's often a bigger risk in not doing it. The challenge is to ensure the initiative works as it should and not just to satisfy any cynics within Masterfoods who simply see it as a way of selling more Mars Bars.
"I admire this initiative because today's consumers are not just looking for product innovation but innovation in the way companies communicate with them.
"Of course, its success will depend to an extent on how well the England team do in Germany. But football teams are more than just a group of players - there are the supporters as well, and if their belief can be encouraged, I am all for it."
DESIGNER - Vicky Bullen, chief executive, Coley Porter Bell
"The Mars 'believe' campaign is successful from a design point of view at two levels.
"First, Mars has ensured it has a visually iconic identity. Like Marmite with the 'love me, hate me' limited-edition packs and Heinz with its D&AD-winning packs, Mars subverts its logo without losing visual recognition or destroying its visual equities.
"Some brands can successfully subvert their logos because of their overall visual qualities. Mars goes further than that - essentially, the packaging identity is the logo.
"This is the second level where it succeeds - it owns a typeface. It is immediately recognisable as being Mars even without reference to Mars."
STRATEGIST - Marco Rimini, director of strategy, JWT
"It's good to see Masterfoods trying to do something different at a time when lots of traditional FMCG advertising on TV is getting less effective. In some ways, it is better than being an official sponsor because you're then committed to spending so much money around that sponsorship.
"The risk in this kind of initiative is you spend a significant amount of money without getting much of a return and I'm not sure that there's an obvious connection between chocolate and football.
"Also, it will not be good news for Masterfoods should England get knocked out early. And the impact of the campaign in Scotland and Wales, whose teams failed to qualify, will, at best, be neutral."
CREATIVE - Steve Henry, chairman and executive creative director, United London
"It's very easy to be disparaging about an initiative of this kind, but I applaud it and I don't see any major risks attached. After all, the Mars Bar is so iconic no-one is going to forget what it's called or what it looks like in a month.
"The only downside is if England suffer an early knockout. If that happens, I hope Masterfoods has a back-up plan and can get the more familiar Mars Bars back on the shelves fast.
"On the other hand, if it's 1966 all over again and the country becomes infatuated with what's going on in Germany, Masterfoods' bravery will really pay dividends."