The great Hungarian coach Bela Guttmann was a firm believer that football managers shouldn't stay anywhere for more than three seasons. He always insisted that "the third season is fatal." Sir Alex Ferguson's career at Old Trafford has made a mockery of that statement.
For 27 years Ferguson has ruled the roost at Manchester United. During that period the club has experienced some of its greatest successes, including two European Cups, 13 Premier League titles and five FA Cups, just to name a few.
But just what has made the 71-year-old Scot such a dominant figure for such a sustained period? What has been the one big secret behind his success?
For me, the big secret is a fairly simple one: Sir Alex Ferguson is football's greatest chameleon.
Whilst Guttmann believed that after three years familiarity would breed a slackness and an apathy, Ferguson has treated such familiarity with utter contempt throughout his time at Old Trafford, and his ability to consistently evolve has led to his 27 years at the pinnacle of the English game.
This ability has been shown in a number of ways, but for the purposes of this article, we'll focus on perhaps two of the main assertions.
The first presentation comes with regards to player turnover.
When Ferguson's most promising pupils, Messrs Beckham, Scholes, Butt and the Neville brothers, were ready to complete their progression into first-team regulars in 1995, Ferguson showed no sentiment to experienced players such as Paul Ince, Mark Hughes and Andrei Kanchelskis.
Instead, he made room for his fledgling stars to join the likes of Ryan Giggs, Andy Cole and Roy Keane in the first team. Ferguson's faith was duly rewarded with a Premier League title at the end of that first season, and those players would go on to be the backbone of the 1999 treble winners.
Additionally, Ferguson has never shirked ridding the club of players whom he believed had become more trouble than they were worth, no matter how they were perceived in the stands. Ruud van Nistelrooy, Dwight Yorke and the aforementioned Ince have all fallen foul and been shown the exit door, thus allowing others to come out and flourish in their place.
Perhaps the most shocking departure of all was legendary skipper Roy Keane, who was bombed mid-season in 2005 after giving an interview to United's in-house television station which was extremely critical of the club's younger first-team members.
The United boss has never shirked major decisions over his players, and has therefore always held dominion at Old Trafford, in ways that many managers at other clubs could only dream about. No player has ever been indispensable, and when greats have left, the side has always advanced in a new way without them.
Another such way, perhaps the greatest way, in which Ferguson has shown his Chameleon-like ability has been through the tactical evolution of Manchester United with him at the helm.
Pre-1994, Ferguson was a devout 4-4-2 man. However, a European Cup hammering at the hands of Johan Cruyff's Barcelona saw United's midfield taken to pieces in a 4-0 defeat. From that Ferguson began to experiment, adding an extra man in midfield, or splitting strikers with a 4-4-1-1 formation (Cantona behind Cole, Yorke behind Cole).
There has never been a time when Ferguson has allowed himself to stand still. He has always been looking to change with the times and as such has constantly been willing to learn from others—the likes of Arrigo Sacchi, Cruyff, Louis van Gaal, Ottmar Hitzfeld.
In the early-mid noughties, when the Arsenal versus Manchester United rivalry was at its peak, Arsene Wenger built an Arsenal side (pre-Emirates Stadium) whose counter-attacking and transition play was the envy of a nation. Ferguson went on to improve on that, with a side who, between 2007-09, were quite probably the greatest counter-attacking force in Europe.
Throw in the fact that United's Champions League winners of 2008 didn't really play with a fixed reference point at the centre-forward position; Carlos Tevez, Wayne Rooney and Cristiano Ronaldo often occupied the three most attacking positions, but none offered a static central presence.
In that respect, Ferguson was something of a trendsetter, employing what has commonly become known as the "false-nine" before it became fashionable (although he of course wasn't first amongst major European clubs to do so, Luciano Spalletti's Roma having starting using Francesco Totti in that role from the middle of the 2005-06 campaign).
To continue ensuring that he and his United side have remained relevant, he has also sought out intelligent coaches to work alongside him. From Brian Kidd and Steve McClaren to Carlos Queiroz and now Rene Meulensteen, Ferguson has always surrounded himself with tactically astute "football people" whose skill sets cooperate well with his own.
It's a commonly held conception of human nature that people fear what they can't understand. Over 27 years at Old Trafford, Ferguson has not only sought to understand the changes of the footballing world, but also to embrace and adapt with them.
Ferguson's great strength over 27 years at the peak of English football has been to evolve with the future, whilst simultaneously competing in the present. Even in his 72nd year, constant adaptation has enabled him to prosper.