I've had endless after-hours discussions regarding that million-dollar question: what drives fashion on, and who decides when is the tipping point?
Some argue it's all down to image-makers, such as Steven Meisel, Tom Ford or Carine Roitfeld.
Others insist it's trailblazing designers such as Miuccia Prada, who can be relied upon to come up with fresh ideas every six months.
Although no one would dare challenge the notion of the international catwalks being the birthplace of new fashion (editorials merely report on these), it takes a few more ingredients besides extraordinary clothes, son et lumière theatrics and clever hair and make-up trickery to successfully bring fashion to life. Vital to producing any new look is finding the right model at the right time.
I always argue that the one person directly responsible for pushing fashion on for the past decade, ever since his collaboration with Prada first began, is the catwalk model casting director and Svengali, Russell Marsh.
No one besides Marsh, with the exception of Meisel, has been more successful in his quest for discovering models' talent that in turn become a living canvas for whatever is the next fashion movement.
It's no coincidence he has the ear of designers such as Prada (Christopher Kane is another who employs him).
Blame Marsh for booting out the curvaceous Brazilians in the late 1990s in favour of the Eastern European waiflets who have since dominated the international catwalks and designer campaigns.
I can well remember witnessing Sacha Pivovarova's Prada runway debut strategically engineered by Marsh, who found her at the age of 16.
Looking back she was (then) so different from any other model I had ever seen. Almost alien. Hmmm, I thought. What is Russell up to? Fashion is about to change. And it did. Now Pivavarova has not only triggered so many model look-alikes, her face staring back at you from magazines no longer appears to be high fashion. Her type of beauty has even been embraced by L'Oreal TV adverts.
Marsh's choices for Prada and Miu Miu are scrutinised each show season for good reason. Ignore his choice of girls and you may as well stick your head in the sand.
This September, slightly out of the blue, Marsh decreed it was a case of "all change" once more. From nowhere, the exotically named Arizona Muse not only opened (and closed) the Prada show, she went on to be the break-out star of spring/summer 2011 shows including Chanel, YSL and Dior. No wonder Muse has since become the latest fashion it girl.
With her impossibly high cheekbones and alabaster skin, the blonde beauty could have come from anywhere in Europe (or Australia or Brazil). Even more shocking than her catwalk domination was the fact that she hails from a continent whose once plentiful supply of super-league models was thought to be going the way of its bison: the US.
Although one could hardly describe Muse's "look" as all-American (she actually is more a young Jane Birkin), she is undeniably pretty. When was the last time you could say this about a high-fashion model without adding "but she's way too..." followed by the relevant adjective, ranging from scrawny to scary/cool/weird.
The 19-year-old was joined by a fresh line-up of first-season new faces, including Maddie Kulicka, Hailey Clauson, Joan Smalls and Caroline Brasch Neilson, who are now tipped to clean up in terms of spring/summer 2011 campaigns.
What do we know of Muse? Her real name is Zoe Muse. She's American. She's a mother to an 18-month old son called Nico. She did have waist-length hair pre-Prada, now it's hewn to a stylish bob. She was discovered in LA in 2008 when she was 17 and waited a year to beging ner modelling career so she could finish school. She is now represented by the model agency Next and jets between homes in LA and Paris.
It's not just the fact she snaffled the best outfits in the key shows that the entire industry is watching to see what she does next.
If she had stepped blinking into the Milan sunshine following her triumphant Prada debut to face the waiting paparazzi wearing something intrinsically dull, things might have been very different.
As it was, the off-duty Arizona get-up of wrinkly velvet boots, ditzy scarves, kooky Bloomsbury style hat pulled down low teamed with a pretty farm-girl dress was documented by the paparazzi, already sensing a new star.
This year's model, according to the editorials is Freja, possibly Lara. Next year's, decreed by the man who pulls the puppet strings of fashion, is Muse.