Sir Alex Ferguson's ability to adopt and adapt was fundamental to the longevity of his success as Manchester United manager.
With his haul of 13 Premier League titles coming across 21 seasons, Fergie is unquestionably one of the greatest managers of all time, not only because of the quantity of trophies he delivered, but also because he maintained such an impeccable standard over such a long period.
Ferguson achieved this by quickly and mercilessly sensing the need for change. During his entire 27-year reign at Old Trafford, Fergie employed seven different assistant managers, all of whom were hired to bring fresh ideas to the table and change power dynamics on the training pitch.
The Scot was also ruthless when it came to squad building, often selling seemingly crucial, world-class players the moment he became concerned over their performances, focus or commitment. In other instances, key players were sold for tactical reasons, the biggest example being Ruud van Nistelrooy.
The Dutchman scored 150 goals in 219 appearances for United, including 24 in his final season, but could only fire United to a single Premier League title in five years, and his limited playing style - which focused entirely around converting chances and otherwise doing very little - contrasted greatly with the growing trend of mobile, fluid, aggressive, all-round forwards. Tellingly, after van Nistelrooy left for Real Madrid, Fergie's new-look frontline consisted of Cristiano Ronaldo, Wayne Rooney and Carlos Tevez.
But fast-forward three years to when Ronaldo made the same move as van Nistelrooy by trading the Red Devils for Los Blancos, and Ferguson's view on finances in modern football inadvertently set up Real Madrid for an era of unprecedented dominance in the Champions League. Because it wasn't only CR7 United had to make a big decision on that summer - they also had to make their minds up on then-Lyon prodigy Karim Benzema.
Real Madrid's European Dominance and Generational Strike Force
Cristiano Ronaldo in Real Madrid kit looking angry - with Real Madrid theme/logo
Having made it past the Round of 16 just once in five seasons, Real Madrid were ready to do something different in summer 2009. They went on an unprecedented spending spree, shelling out a total of £227m on some of the best young players in the world - Benzema, Ronaldo, Kaka and Xabi Alonso.
There wasn't an instant improvement; Real Madrid finished the season in second in La Liga and crashed out of the Champions League in the Round of 32. But when Jose Mourinho replaced Manuel Pellegrini in the dugout a year later, by the end of his first season Los Blancos had reached the semi-finals for the first time since 2002/03.
They would reach the same round in subsequent years, before winning the European title under Carlo Ancelotti in 2013/14. That was followed by an era of unprecedented dominance by modern standards, when Zinedine Zidane led Real Madrid to three consecutive Champions League titles in 2015/16, 2016/17 and 2017/18.
There were many elements to Real Madrid's UCL-retaining team, which boasted world-class quality in almost every position. Sergio Ramos and Pepe formed an iconic centre-back partnership, Marcelo is one of the greatest left-backs of all time, Toni Kroos and Luka Modric were technical masters in midfield, and Gareth Bale - when fit - was a force of nature on the big stage.
But fundamental to their success was Ronaldo and his attacking accomplice, Benzema. Despite being a world-class goalscorer in his own right, the French centre-forward sacrificed much of his own game to facilitate Ronaldo. But it was impossible to dispute the end result. From all the Portuguese's career team-mates, Benzema ranks highest for joint goal participations with Ronaldo at 73 from 342 games, and in total, they scored 522 goals while playing together.
It could've all been very different, however, had Fergie taken a different view on football finances back in summer 2009.
Ferguson didn't Anticipate the Need to Meet Inflated Transfer Fees
Karim Benzema in action for Real Madrid
Karim Benzema in action for Real Madrid
Benzema was one of the players at the top of United's shopping list in summer 2009, but as the Red Devils failed to adapt to the sudden inflation in worldwide transfer fees, the Red Devils ultimately ended up signing Michael Owen on a free transfer instead.
With Rooney and Dimitar Berbatov already part of the squad, it wasn't essential that United signed a first-choice forward that summer. Nonetheless, Fergie's evaluation of Benzema from the time makes very interesting reading now; bemoaning Real Madrid's willingness to take on debt to sign the world's top players, he questioned whether there was value to be had in their £35 splurge on Benzema.
"We went in for Benzema but, as far as we were concerned, the price tag was beyond his value. If other clubs want to go to that level, that's entirely their business. We had a value that we thought was fair and we didn't want to go above that position. Maybe Lyon thought we under-valued him and that's fine, it's their decision. They got €42m for him and they will be happy with that because they have done well. All this tells you about us is that we are sensible."
In fairness to Ferguson, spending £35m on a 21-year-old striker playing in the French top flight would be a bit of a gamble now, let alone back in 2009 when transfer fees were generally much smaller. But in subsequent seasons, such pricing would become the norm, especially for young players with enormous potential. Fergie, however, was adamant that United needed to spend sensibly in defiance of 'stupid' prices in the transfer market.
"Some of the values across the world now are amazing; the numbers that get tossed about. The values of players have shot sky high. I don't think any of the [big] transfers this summer are realistic but for some reason it has caught fire this summer. It's an unusual summer and it's very difficult to get value because of that."
"I can only placate the fans in one way and that's by not being stupid. We have that wonderful sum of money from Real Madrid but there's no way we are going to throw it away by putting an extra zero on the end of transfer fees when I didn't think it was value."
The problem was that it wasn't only that summer; this type of pricing very much became the norm and even within the space of twelve months, Liverpool and Chelsea had matched Benzema's transfer fee by signing Andy Caroll and Fernando Torres. A year later, City spent a similar sum on Sergio Aguero.
United, meanwhile, shied away from big investments and instead focused on Premier League-proven signings at mid-range transfer fees - Namely Antonio Valencia, Chris Smalling, Phil Jones, Ashley Young and Robin van Persie - or cheaper punts on younger players, like David de Gea and Wilfried Zaha.
But none of them would cost as much as Benzema and although many proved to be solid club servants, only De Gea threatened to enjoy world-class status for a consistent period of time at Old Trafford. Fergie managed to win two more Premier League titles and reach the 2010/11 Champions League final, but lacking the next breed of best-in-class players at their peak, United quickly dropped off once he'd retired.
Indeed, while Real Madrid won the Champions League in 2013/14, the Red Devils failed to even qualify for the subsequent tournament, and when Los Blancos started their run of three consecutive crowns in 2015/16, United were instead winning Europe's secondary competition, the Europa League.
Many United fans will point to the Glazers' role in United's finances and their lack of big spending dating back even further to the Americans' takeover in 2005. But it's clear Ferguson himself was wary of modern transfer fees too, and seemingly feeling summer 2009 was the outlier rather than the rule, he only invested a portion of the Ronaldo money, opting to hold onto it rather than reinvest in Benzema - a future Ballon d'Or winner.
It wasn't until much later that the impact of Fergie's stance became more evident; while United's ageing squad completely fell apart in the immediate aftermath of his departure, Benzema and Ronaldo were making Real Madrid the kings of Europe.