There is one relatively straightforward explanation for the perplexing decline of Novak Djokovic, and it doubtless holds water.
Having reached his main career goal of being French Open champion last June, meaning he had the astonishing distinction of holding all four Grand Slams at once’, he suffered an existentialist crisis of motivation. What else was there left to achieve and to make all the sacrifices for?
Yet, there must be other factors involved, some probably connected to that. They have resulted in the outcome that saw his Melbourne Park citadel stormed by Denis Istomin, a journeyman from Uzbekistan with zany eyewear.
For instance, after he won the Qatar Open final against Andy Murray a week last Saturday, Djokovic returned home to Monte Carlo, rather than hotfooting it to Australia along with everyone else, Murray included.
He only arrived in Melbourne on Wednesday morning, and is said to have cancelled late on one of his main sponsors for a dinner they had planned around him on the Tuesday night.
Djokovic has made clear that he is currently prioritising spending time with wife Jelena and their son, and admitted at the US Open that personal problems had surfaced in his life during last summer.
Jelena has not been in Melbourne, and while flying home was a powerful display of his commitment to her, heading in the opposite direction to everyone else after Qatar was a strange way to prepare for a Grand Slam.
Trying to get one’s life in kilter is a natural enough urge for anyone, but it is not necessarily conducive to the rarefied business of trying to win Grand Slams.
Then there are the suggestions from within the locker room that Djokovic is not in prime fighting shape. Insiders have noticed some weight loss from his wirey frame and it certainly looks with the naked eye like he has lost a few kilos.
He has long since obsessed about his diet, and is always keen to experiment. He talked this week about how he might open an Australian offshoot of the vegan restaurant he has in Monaco.
Djokovic was accompanied here by his old faithful, Marian Vajda, but there was no sign of his Spanish coach-cum-spiritual guru Pepe Imaz. He has become increasingly influential and was with him at the 02 Arena at the end of last season.
The impression is one of instability and of a man searching for answers to some profound questions. Djokovic has been a ruthless champion but he is not a shallow person, and it is legitimate to ask whether a form of burnout has set in after giving so much of his life to the sport.
He would not be the first such case at the top of tennis, and many of the greatest players have found the grinding commitment hard to maintain. Bjorn Borg, not someone with the same intellectual curiosity as the extremely bright Djokovic, is an oft-cited example but there are others.
The men’s game is a deeply unforgiving world where any weakness is pounced upon. From holding all four Majors he is now down to just one, with Murray the main beneficiary.
The 29 year-old Scot, due to play against Sam Querrey, is now all but guaranteed the world No 1 spot until at least the spring, regardless of how he fares this fortnight.
Murray was quickly installed as marginal odds-on favourite for the title ahead of his match against Querrey, now that his nemesis at this event has gone.
Djokovic was unclear in the immediate aftermath where he will surface next. February is one of the tour’s quieter months, heading into March’s two Masters events in America and then the long wind up of the European clay court season.
There is not a lot to get motivated for in the coming weeks at the best of times for someone like him, so he will have plenty of time to reflect.
However well Istomin played, this was not the Djokovic we are accustomed to seeing in Melbourne, breaking Murray’s heart and digging deep within himself.
The Uzbek had two set points in the second set, so it was not that he did not have chances to win the match more easily.
What was truly admirable was the way that he nervelessly kept hitting out and driving on in the decider, when many players would have been intimidated by the great champion at the other end.
But then he knows that the Serb is not the near-invincible fighter that he was once was, and auras can disappear quickly in this sport.
While he had arrived here having beaten Murray in Qatar he would never have even been in the final had Fernando Verdasco not choked five match points in the semi-final that proceeded it.
In technical terms he has been playing more conservatively, and the laserlike backhand down the line that was one of his great weapons is not functioning with the consistency it once did.
So there he was on Thursday, beaten by the man whose only other tournament this year was a second round loss in a Bangkok Challenger event to someone ranked outside the top 200.
Coached by his mother, he sweetly thanked her on court afterwards for the good job she had done with him.
Less than a year earlier, Djokovic had held the trophy aloft with Murray, his face like thunder, in the background. Now he had lost for the first time at a Grand Slam to someone ranked below 75.
Men’s tennis is due a left field Grand Slam winner, and if Murray slips up this could yet be the event that provides it.
EDITED FROM: dailymail.co.uk