A couple of years ago, Sir Alex Ferguson was musing on the cyclical nature of success.
"I always believe a four-year cycle is probably the most you can achieve," he said. "There are very, very few teams who can create more than a four-year cycle."
There are a few clubs, however, or a few managers, who can become masters of sustained success. They can create a dynasty. Over the Premier League's two decades, Manchester United have won 12 titles, not to mention two Champions Leagues.
In one respect, the most obvious four-year cycle in that time was the exception to the rule: the four-year gap between 2003 and 2007, between Ferguson's eighth and ninth titles.
It is the only time in the past 20 years that they have gone successive seasons without being officially England's best team. That is a sign of United's powers of recovery: normally when deposed, their immediate response is to reclaim their title. United are rarely more dangerous than when their pride has been wounded.
It certainly was by injury-time events at Manchester City on May 13. United finished their own game at the Stadium of Light as champions elect. A dramatic turnaround later, they had been overhauled by their neighbours.
It adds a local flavour to a familiar battle, to knock someone else off their particular perch. Yet Ferguson's own theories pose a question of where the modern-day United rank. Conventional wisdom is that he has had three great teams, although the class of 2003 certainly merit a mention in the same company.
That the sides of 1994 and 1999 deserve such a billing is beyond doubt; so, too, Ferguson's finest recent ensemble, who reached their peak in 2008.
That, as even a rudimentary grasp of maths shows, is four years ago. A quick comparison does not flatter the majority of current crop: Edwin van der Sar has retired and David de Gea is an uncertain, if able, replacement. In 2008, Patrice Evra, Rio Ferdinand and Nemanja Vidic were three-quarters of an outstanding back four. Age and injuries have taken their toll, even if there is the hope that the Serb, now fit again, can provide an action replay of his imperious form in the 2010/11 campaign, when he was the outstanding defender in England.
And then there are the two veterans. In the bowels of the Luzhniki Stadium in Moscow, after making United European champions for a second time, Ferguson spoke of phasing out Paul Scholes and Ryan Giggs. If anything, they have not merely retained their significance, but increased in importance. The Welshman has played more than 150 times since then, the Englishman has returned from retirement to become a cornerstone of the midfield again.
Like Ferguson's continuing prowess, their extended excellence is a thing of wonder. It is also a cause for concern. In midfield, United seem disproportionately dependent upon a 37 year old and a 38 year old.
And yet there is one department where United have players at the peak of their powers and it is where titles are often decided: attack.
Wayne Rooney scored 35 goals for United last season, Robin van Persie 37 for Arsenal. By paying £24 million (Dh138m), Ferguson has united them in attack. For the first time since Cristiano Ronaldo's 2009 sale to Real Madrid, they have recruited a replacement of proven class. There is a hint, too, that something else will change. Shinji Kagawa should provide goals from midfield, an area where United have tended to be outscored by their rivals in recent years. Factor in Van Persie as well, however, and they look far more prolific.
Realise that Vidic, limited to a handful of starts last season, is fit again and the defence should tighten up. Suddenly United appear stronger in all departments.
And it is worth remembering, too, how close they have come during the interregnum between Ronaldo's exit and Van Persie's arrival.
Had Rooney not injured his ankle in Munich in March 2010, the year Chelsea topped the league, and but for the extraordinary events in injury-time on the final day of last season, United would have won an unprecedented six consecutive titles. They ended last season with 89 points, a record for a second-placed side. A winning habit remains entrenched, Ferguson's refusal to accept defeat personified by players new and old.
Plenty of Old Trafford regulars will willingly accept that side was not a patch on many of their predecessors, but they retained the invaluable ability to get results.
Even something as uncharacteristic as letting an eight-point lead slip in last season's title race had the feel of an isolated aberration, not an indication of more widespread problems.
Whereas in 2005, during Ferguson's four-year drought and his most troubled times at Old Trafford since his initial difficulties, predictions of his demise abounded, few have made that mistake again.
He is 70 and approaching his 26th anniversary at Old Trafford, but is rarely deemed yesterday's man. Yet his own analysis, his past talk of a four-year cycle, raises the question of where United are.
The signing of Van Persie, his biggest statement of intent for many a year, gives United an unrivalled amount of firepower. History suggests a relentless winner will pedal back to the top at the first time of asking.
The resolve and record of the most decorated manager of all time to overhaul City suggests that, while Chelsea are the biggest spenders and Roberto Mancini has arguably the strongest starting 11, United will respond the way they normally do to a setback.
Forget four years, it often only takes one.