Joseph scales the heights in Melbourne
There's such an old-school reticence to how the O'Briens conduct themselves in the face of epic achievement that the temptation is forever there to mistake them for unremarkable people.
Joseph is clearly cut from his father's cloth, as a spellbound media found in Melbourne early last month, intercepting the amazement of the outside world with what can seem almost exaggeratedly bashful humility.
The numbers continue to signpost Aidan O'Brien's genius, yet he has long established a relationship with the outside world that is founded, first and foremost, on good manners.
That's not an everyday quality in professional sports environments so heavily soaked with finance that empathy with those hard-pressed by mundane stuff like household bills and loan repayments eludes so many.
Bear in mind that Rekindling's remarkable victory in front of 90,000 people (not to mention a spellbound nation) at Flemington Racecourse brought home a prize pot of $3.6 million to its connections.
That exceeded the total take of all Joseph's previous winners in his mere 18 months working out the possibilities of Flat and National Hunt horses from that hill in Piltown off which his father and grandfather made their names.
Even those of us less than intimate with the equine world can't but recognise that a 24-year-old training the Melbourne Cup winner pretty much decommissions any sensible argument about the greatest Irish sporting achievement of 2017.
Bear in mind that Joseph O'Brien was born the year Dermot Weld did what most presumed no northern hemisphere trainer could ever do, winning in Melbourne with Vintage Crop in 1993.
Joseph came into this world just two weeks before his father, who has since rewritten just about every record in the Flat world, trained his first winner. He was a wide-eyed nine-year-old when Weld then won another Melbourne Cup with Media Puzzle in '02.
Yet, Joseph's entire childhood was so wrapped up in Ballydoyle and its relentless march that an inherited understanding of thoroughbreds was, maybe, always going to push him in the direction of succession.
That said, understanding is one thing, a man writing his own history is quite another.
Irish racing now exists at an altitude that makes it almost difficult to remember there was a time when the idea of trainers from this part of the world taking their chances at Flemington was considered the equivalent of going into the water after crocodiles with waders and a net.
Incredibly, five Irish-trained horses finished in the first ten this year, three of them trained by National Hunt wizard, Willie Mullins.
Aidan himself saddled Johannes Vermeer to runners-up spot, watching history unspool at home in Tipperary, where he admitted he found himself "hoping and praying" that his son's horse would win.
There'd been little indication that Rekindling belonged in this kind of company last year when in the yard of David Wachman.
But moved to Joseph's care, different windows began to open. Rekindling won at Grade Two level in The Curragh but, when entered in The Derby last June, he came home third last. The three-year-old then went to Doncaster in September, finishing fourth in the St Leger.
Australia was now in owner Lloyd Williams's thoughts, yet so too was the worry that a young horse in training from April to November might be tiring.
To that end, the young trainer's counsel became decisive.
Williams, for whom it was a record sixth victory in Melbourne, would suggest Joseph's training achievement was "close to being able to walk on water".
Rekindling, after all, became the first three-year-old to claim the big prize since Skipton in 1941 and Joseph, unsurprisingly, registered as the youngest-ever winning trainer.
The sheer scale of that achievement is maybe difficult to contextualise given the weight of Irish numbers at the front of the field, prompting Patrick Mullins, Willie's son and assistant trainer, to joke that they'd travelled to the far side of the world only to be beaten by horses "from down the road in Kilkenny and Tipperary".
Rekindling became the first horse since Vintage Crop to win the Melbourne Cup without having run a prep race in Australia and, in doing so, ignited a natural debate about just how high his young trainer might now climb in that kind of rarified air.
In many ways, Joseph O'Brien defied genetics as a jockey, engaging in an unnatural fight with his own frame to make the weight and win the Epsom Derby for his father on Camelot (2012) and Australia (2014).
The cruel, ascetic demands that life in the saddle placed upon him became the faintly joyless subtext to those glories, a subtext he admits now that he doesn't miss "in the slightest" as his training career gathers such thrilling momentum.
What could he become?
It is a giddy question given the clear evidence that his understanding of horses is already pitched at a level invisible to all but the most gifted eye.
True, natural, compelling arguments may be made in these pages for his father Aidan's world-record achievements, Joe Canning's point against Tipperary, Seán O'Brien's try for the Lions, James McClean's goal in Cardiff, Con O'Callaghan's deft finish against Mayo, Katie Taylor's world title win, maybe Paul Dunne's magical closing round of 61 to win the British Masters in Newcastle. But Joseph O'Brien saddling Rekindling to win the Melbourne Cup simply took things to another place.
It left his sport all but speechless at the brazenly sharp judgement of a young man who has inherited so much more than simple good manners from his parents, Aidan and Anne-Marie.
He has taken from them the compulsion to hunt down history. And his story has scarcely run past its opening chapter.