Have you heard the news? Avatar is going to make the blind see. It'll stop you catching swine flu. It'll make you irresistible to potential partners, rich beyond your wildest dreams and, heck, probably immortal.

OK, nobody from 20th Century Fox has actually come out and said that yet, but it's only a matter of time. The hype surrounding Avatar has been slowly building for years now. This weekend, a 25-minute Avatar preview was shown at Comic-Con by director James Cameron. 21 August is going to be named Avatar Day, and it'll be marked by every Imax cinema in the world (or as many as Fox can commandeer) showing 15 minutes of Avatar to fans for free. The Avatar videogame and action figure set will also be unveiled. And that's all happening four months before Avatar is even released (it's out in December). How can Avatar manage to ramp up expectations even further in the ensuing months?

James Cameron seems like a man seldom troubled by self-doubt. Every time he's nudged the movie industry forward with films such as Terminator 2 or Titanic – or women's rights back with films like True Lies – he's done so with a swaggering, cocksure, king-of-the-world confidence. And rightly so, you might say, given his track record.

However, if he's not careful, Cameron's swagger might start being mistaken for a full-body nervous tic. Ever since he announced Avatar, a film he's been prepping for 14 years, anticipation has been building steadily. Thanks to the technical specs – it was filmed with 3D virtual cameras using groundbreaking photorealistic motion-capture animation technology – and the paucity of information or footage released, fans have been greedily lapping up whatever scraps they can get. And when those scraps include Jon Favreau calling it "the future" of film-making, that's setting an expectation that even James Cameron might find difficult to meet.

And that might just explain Avatar Day. First, it will give James Cameron the luxury of allowing the film footage to be seen in a way that does the movie justice, rather than just allowing a tiny trailer to be leaked on to YouTube. Presumably Avatar Day will also serve as a wake-up call to cinema chains, showing them that digital 3D won't simply be a gimmicky flash in the pan and giving them four months to convert and allow them to share the rewards that Avatar will offer.

But maybe Avatar Day is also meant to consciously dampen expectations, too. At the moment, following the frothing, celebratory 25-minute Comic-Con preview, the public at large would be forgiven for thinking that Avatar is not just a quantum leap forward in terms of film-making, but also the dawn of a new chapter in the history of mankind.

However, by giving the public 15 minutes of Avatar for free, perhaps James Cameron wants everyone to realise what Quint from Ain't It Cool realised this weekend – that Avatar is "good, layered, incredibly detailed and full of imagination and incredible imagery ... just don't expect to have your head blown out your asshole or eyeballs raped or whatever the newest talkback thing is".

And that might be the smartest thing that James Cameron could have done.