When Mariah Carey recorded All I Want For Christmas Is You 20 years ago this month, few could have foreseen that it would become one of the world's all-time festive favourites.
But that status is in no doubt today, as the track became only the ninth Christmas tune to sell one million copies in the UK yesterday.
The enduring success of All I Want For Christmas Is You should not be a surprise though. Whether because of Mariah's iconic video (frolicking in the snow, wearing her Santa-themed micro dress), the recording's upbeat joyfulness or the timeless quality (even though it was produced and written by Mariah with Walter Afanasieff), the track has something for everyone.
But it is also a key beneficiary of the huge shift in music consumption over the past decade, from physical CDs to digital downloads.
On its first release, All I Want For Christmas Is You peaked at two, sold around 300,000 copies, hung around the Official Singles Chart for eight weeks and then disappeared.
Like all singles back then, it was then resigned to life as an annual radio staple and occasional feature on Christmas compilations. But when digital downloading began to take off in the mid Noughties, all that changed.
Suddenly, every single ever pressed could be available forever - as a download on iTunes, Amazon MP3, 7 Digital, Tesco Digital and HMV.com. For Christmas songs particularly, this was a gift.
Since 2007, Mariah's jaunty hymn has hit the Official Singles Chart every December, as revellers across the country pull together their playlists and (like their tinsel and baubles) realise they can't find their favourite track from last year.
Across those seven years (from 2007 to 2013), it has consistently sold 80,000 plus copies, year-in, year-out. And it is not the only one, of course - the Pogues Ft Kirsty MacColl's Fairytale of New York sells more than 100,000 copies every year, all driven by our love of nostalgia.
Of course, none of us should be in any doubt about the British public's love for a cheesy Christmas chime, the evidence is all around us. Every year the British nation embraces the race for the Christmas Number One - and nine relentlessly Christmassy songs have reached a million sales over the past 61 years (from versions of Mary's Boy Child by Boney M and by Harry Belafonte, through to tunes by Band Aid, Slade, Wham!, Bing Crosby and Mariah). Downloading has simply let this love run free.
The impact of this annual frenzy for party tunes on the overall music market is immense. In the past 10 years (according to new research conducted by the Official Charts Company) a total of more than 15.4million Christmas tracks have been sold digitally (spanning festive songs and Christmas Number Ones past and present).
In turn, a range of key tracks, including classics from Carey, the Pogues, Wham, Wizzard, Slade, Chris Rea and Shakin' Stevens, sell together around 500,000 copies every year - as they re-establish themselves on playlists across the country and re-enter the Official Singles Chart.
We've always known that British music fans LOVE their Christmas tunes, but this new analysis shows just HOW much. We certainly are a nation of festive classic fanatics.
It is for this, very understandable reason, perhaps, that we have started seeing a resurgence of interest from artists looking to create their own new Christmas classics. In recent years, Michael Buble, Stacey Solomon, Rod Stewart have all had a shot; this year, Leona Lewis, Susan Boyle, Richard & Adam and Mary J Blige have joined the party.
None of which is surprising, of course. Create a Christmas song which connects with the public and you will have a resurgent hit with years (perhaps decades) of life ahead of it.