O’Brien’s achieved a huge amount in a short space of time, but has an ongoing battle with the scales, which he currently seems to be just about losing.
That’s hardly a great surprise and the fact the young man has literally defied nature for so long has been nothing less than extraordinary.
He will be 22 next month and stands some six feet tall. Last season he was able to do 9-0 and that was almost a miracle.
Indeed, remarkably, O’Brien did 8-12 at York in August when partnering Australia to land the Group 1 Juddmonte International Stakes.
But, over seven months later, the evidence at the moment is that he clearly faces a tough struggle to get back to where he wants to be.
O’Brien rode his first winner in May of 2009 on Johann Zoffany at Leopardstown and then proceeded to make a rapid rise through the ranks.
Of course he had the massive backing of his father, Aidan, and Ballydoyle, but repeatedly showed he was more than equal to the many high profile tests that were put in front of him.
Obviously, there were blips along the way, the most notable probably being the defeat Australia suffered at the hands of The Great Gatsby and Ryan Moore in the Irish Champion Stakes at Leopardstown in September.
But, overall, there haven’t been many days when Ballydoyle horses were beaten and the finger could then be pointed in the direction of O’Brien.
He was champion jockey for the first time in 2012 and the following year retained the title, with a record 126 winners.
O’Brien has won the Epsom Derby and the Irish Derby on two occasions, with Camelot and Australia.
He has taken the Irish 2000 Guineas three times and the English equivalent once, with Camelot.
A Breeders’ Cup came his way aboard St Nicholas Abbey and Leading Light gave him success in both the Ascot Gold Cup and the English St Leger.
Basically, the young man has nothing to prove, but that is hardly the main point. He was bred to be a jockey, from both sides, and, you suspect, probably never wanted to do anything else.
Up to now he has essentially led a charmed existence and been able to fulfil many of his dreams.
Some of that, however, has been taken away from him, through no fault of his own. If you weigh in at say fourteen stone then shedding 14lbs is not much of a problem.
But Joseph is set to ride at 9-5 at Cork today and trying to lose another 5lbs off that is a massive task.
All the evidence is that he clearly has an iron will, is totally dedicated to his profession and seriously disciplined.
But when you are the height he is, and already exist on a diet that would drive most of us bananas, there is little or no room for manoeuvre.
Ballydoyle has wasted no time getting Ryan Moore very much on board and the fact he was in action for them at Dundalk on Wednesday night was a clear statement of intent, from both sides.
In the meantime, Joseph seems certain to continue the good fight. Hopefully, the more he rides the easier it will be for him to control his weight and if manages a winner at Cork — more than a possibility — is guaranteed a warm reception.
But if he can ever get back to riding at 9-0 again then that will represent just about his best performance to date!
At Cork nine days ago a horse called Roumanian, having a first outing for Willie Mullins, contested a 20-runner handicap hurdle.
He is now a nine-year-old and had previously only run five times on the track.
Roumanian shaped as just about useless in those five races and was beaten a total of 349 lengths.
Prior to Cork, he had been seen previously at Roscommon in July of last year, finishing 15th.
At Cork, he went off a well-backed 11-8 favourite, a comical and astonishing price, considering what he was bringing to the table.
The “wide boys’’ were out in force to lay him — perfectly understandably — on the basis that not even Merlin The Magician could get him to win.
But win he did, travelling like a dream for most of the two miles, before having to get the full treatment from Danny Mullins in the closing stages to score by a short head.
The handicapper then did his work and promptly hiked Roumanian up by 10lbs, which was fairly draconian, on the basis the horse won with practically nothing in hand.
So, logic now dictates that there is no way Roumanian can win again over hurdles-off his new mark.
The problem with such thinking, of course, is that he is trained by Willie Mullins!