As far as followers of British sport are concerned, 2013 has so far proved to be a reality checkpoint.
Less than a year on from the heady glories of the London 2012 Games, many of the home icons from that unforgettable summer are experiencing one of sport's essential truths: the problem with winning is that people expect you to keep on doing it.
Thus in Eugene, Oregon last week, Mo Farah made the headlines in failing to win the 5,000 metres as he made his IAAF Diamond League season's debut in his home-town event. The double Olympic champion managed a season's best time of 13min 05.88sec, but Kenya's Edwin Soi finished just over a second ahead of him.
In the same event last year, which came shortly before the Olympics, the Londoner had won in a time of 12:56.98, the fastest time ever run in the United States. There were mitigating circumstances. Farah had been suffering from a stomach virus in preceding weeks and had made the late decision to switch from the 10,000m on the previous day in order to give himself an extra chance to rest.
But the headlines around the world told a harsh story - Farah suffers first outdoor defeat since 2011. And Soi's victory underlined the fact that, for those who have reached the peak of their event, the world becomes full of those eager to prove a point. For Farah, maintaining a grip on two events which seethe with African talent is an enormous challenge.
Last summer, the words Dave, Weir and London meant only one thing: gold. But despite his insistence before this year's Virgin London Marathon, where he was seeking to go one better than the record of six wheelchair victories which he shares with fellow Briton Tanni Grey-Thompson, that he was in better shape than he had been at the same stage in the previous year, Weir's final surge in the Mall proved insufficient as four others moved past him, headed by his old bête noire Kurt Fearnley.
Weir insisted he would "bounce back." Farah tweeted a couple of hours after his race in the heartland of his sponsors, Nike: "I'll be back for sure." No doubt both are correct. But for both, the magic spell of 2012 has been broken.
As it has, indeed, for the man who could do no wrong last year - Sir Bradley Wiggins. For those who lauded his achievements in becoming the first Briton to win the Tour de France and following up with gold in the Olympic time trial, the twists and turns of Wiggins' fortunes in 2012 have been painful to witness.
Choosing to focus on the Giro d'Italia rather than the Tour seemed, when it was announced, like a pretty cool move. Why not gather the only remaining big title missing?
But Wiggins is too much of a champion to restrict his ambitions, and before long the 33-year-old was making it clear that he fancied defending his Tour title, and doing so as Team Sky's top rider - a position which appeared to have been promised to the fellow Brit who had worked with the rest of the team on his behalf in 2012, Chris Froome.
While the 28-year-old Kenyan-born rider's labours on his team's behalf were impressive last year, there was a clear and growing sense that payback would be required - Froome at the Top.
When the Wiggins ground to a halt in the Giro, being forced to pull out with a chest infection and an underlying knee problem it was bad enough. But the coup de grace came within a fortnight, when it was confirmed that he was not in sufficient shape to ride the Tour anyway.
That saved much awkwardness, as the Team Sky general manager Dave Brailsford - Wiggins's old Olympic boss - had proved as unrelenting in his pragmatism as his rowing counterpart, Jurgen Grobler, in nominating the younger rider for the lead position at the Tour.
The message from Wiggins - "I'll get this sorted" - carries the same defiance as those from Farah and Weir. And who would bet against him doing so? But again, the magic has been dispelled.
How do you avoid that harsh experience? Well, Wiggins's former Olympic team-mate and fellow knight of the realm, Chris Hoy, chose the only certain method. Having added another couple of golds in London to the four he had already collected at previous Olympic Games, the 37-year-old Scot retired.
While his announcement in April, eight months on from his London victories, may have disappointed the organisers of the Glasgow 2014 Commonwealth Games - who hoped he would provide one last hurrah on home soil at the new velodrome named after him - it was clearly thoroughly considered.
Hoy elected to leave on a high. It's a fine strategy. Perhaps its finest exponent was the Australian, Herb Elliott, who retired aged 24 in 1962 having been unbeaten at the mile and 1500m since 1957. He left the sport as world record holder at both distances, and as Olympic champion.
Elliott's record is perfect, and you can't improve upon perfection. But you can extend it. Which is what Usain Bolt is trying to do.
Today, the man who retained his Olympic 100 and 200m titles in London takes his first serious steps in seeking to maintain his pre-eminence at this summer's IAAF World Championships in Moscow as he runs in the Diamond League 100m at the Olympic Stadium in Rome where Elliott effectively bowed out of top class competition.
At the age of 26 - how can he only be 26??? - the ever-amiable Jamaican superstar has announced he intends to remain the fastest man on the planet up to and including the 2016 Rio Olympics. It's quite some ambition for a man who, after his startling breakthrough at the 2008 Beijing Games, spoke fondly about getting a job where he could put his feet up and take things easy.
Bolt's record fall short of the Elliott Standard in terms of infallibility - he was beaten by Tyson Gay over 100m in 2010, he was disqualified for false-starting in the 100m at the last World Championships in Daegu, and, a few months before retaining his Olympic titles, had suffered a potentially demoralising defeat on home soil by the younger compatriot who had taken that world 100m title, Yohan Blake.
But these are blips in a passage of glory. Now that Tiger Woods has dipped away from the heights he once occupied, Bolt is probably the most pressurised individual sportsman in the world - pressurised, that is, by the expectation he has created himself by his excellence.
The latest challenger to his brilliance - the ever-talkative American Justin Gatlin, back in the sport after a lengthy doping ban - stands ready to apply the dimmer switch in Rome.
Given Bolt's year so far - victory at the Cayman Invitational event on May 9 in 10.09, his slowest ever 100m time, following early-season hamstring problems - this might be an opportunity for his 31-year-old opponent, who ran 9.88 at the Eugene meeting where Farah was eclipsed, to impose what would no doubt be a gleefully celebrated coup.
If that happens, you can be sure there will be a defiant message emanating from Bolt of the kind already offered by Farah, Weir and Wiggins. But first, Gatlin has to find a way of beating him. And that, as a generation of sprinters can testify, is beyond elusive.
Mike Rowbottom, one of Britain's most talented sportswriters, covered the London 2012 Olympics and Paralympics as chief feature writer for insidethegames, having covered the previous five summer Games, and four winter Games, for The Independent. He has worked for the Daily Mail, The Times, The Observer, The Sunday Correspondent and The Guardian. To follow him on Twitter click here.