After the joyous vibrancy of Monday night at Old Trafford, it's incredible to think how jaded Manchester United looked just 10 months ago.
Wayne Rooney wanted to go to Manchester City. The club seemingly didn't want to sign premium-level new players. But, after the late October win over Bursaspor, Alex Ferguson wanted to send a message.
"I had a player once who said to me that Rooney and [Cristiano] Ronaldo weren't good enough and he was not prepared to wait until they were good enough. But that's the trouble with potential. People don't identify potential. They're very poor at it. I've identified all my life the potential in young people. I know potential. I know how to develop and have faith in it. And young people surprise you when given the opportunity. That's what this club is all about."
Considering the events of the time, as well as Rooney's apparent criticism of what the club had come to be about, Ferguson's words seemed no more than an admirable - but ultimately empty - statement of defiance. The average age of the first XI was touching 30 and their performances were barely getting past patchy. With the Glazers seemingly refusing to invest, Rooney's complaints appeared justified.
Typically, though, it was Ferguson who would eventually be vindicated.
A 22-year-old in Javier Hernandez would transform from an impact sub into a Champions League match-winner. The 20-year-old Chris Smalling would mature into a modern defender. Nani would continue his progress from one of the most wasteful players in the Premier League to the most productive and a forgotten Fabio would overtake his twin brother Rafael. At Sunderland, Danny Welbeck was building up the confidence he needed to receive a chance at United while Tom Cleverley was doing the same at Wigan.
One of the results - beyond last season's title and Champions League final appearance - was a thrilling 3-0 win over Tottenham delivered by a team with an average age of 23. United have been, quite literally, rejuvenated.
Amid all the praise for Ferguson's faith in potential, though, it's been overlooked that the average age of Arsenal's team last weekend was also 23.
Or, if not quite overlooked, then predictably viewed through an entirely different prism. Whereas belief in youth has brightened United, it continues to slowly bring Arsenal down from the position they were in seven years ago.
To a degree, the issue seems to define the differences between the two managers. Indeed, two phrases that have been repeated a lot around the Emirates and Old Trafford over the last while are particularly pointed.
In Manchester: "Wenger talks about youth. Fergie just goes and does it."
In London: "We don't need a change in manager, we just need the manager to change."
Either way, both men have always seen investment in youth as their defining managerial traits. And, given that the issue fundamentally boils down to numbers, it's interesting to directly compare their records.
In 25 years at Old Trafford, Ferguson has given 103 young players their debut (for the purposes of clarity, we've included both academy graduates and those signed before the age of 20): that's 4.1 a season. In 15 years at the Emirates, meanwhile, Wenger has blooded 84: that's 5.6 a season.
From those numbers:
• 23% of Ferguson's graduates have played over 30 games for his club; 31% of Wenger's have
• 12% of Ferguson's graduates have played over 100 games for his club; 15% of Wenger's have
• 10% of Ferguson's graduates have played over 200 games for his club; 5% of Wenger's have
• 23% of Ferguson's graduates have succeeded elsewhere in the Premier League or another elite European top flight; 26% of Wenger's have
• 1% of Ferguson's graduates have been sold to a club at Manchester United's level; 7% of Arsenal's have been sold to a club at Arsenal's level
And, perhaps most tellingly:
• 23% of Ferguson's graduates have won medals with his club; 13% of Wenger's have
To a degree, the numbers prove what we already know: Wenger is more likely to initially flood young players into his squad, Ferguson is better at finishing the job - in a few senses. But that also perhaps raises issues about both men's clubs as actual breeding grounds beyond the academies.
When Wenger first arrived at Arsenal, for example, he could neither introduce a nucleus of readymade graduates nor immediately enforce his ideals. Rather, he had to adapt around the existing qualities of that old Highbury core. In the process, though, they all became better players.
The success that mix brought entrusted Wenger with almost total control of the club's playing structure. But it has also meant that, since then, he has altered it so his youth system only produces particular types of players. Famously, Wenger has physical and technical ideals for every position. And the result, effectively, is that Arsenal release a stream of similar prototypes.
Contrast that with Manchester United, where there has always been a huge variety of player styles produced - most notably in this crop. But Ferguson also tends to get the timing of their introduction right. Unlike Arsenal, there's always been a blend of proven winners and potential brilliance - right back to the Double-winning 1995-96 team. Wenger began to forego that complementary mix in 2004. Admittedly, as we've seen with Samir Nasri and Cesc Fabregas, not always by choice.
But then that also raises questions over whether Wenger has created a damaging cycle for himself. Indeed, one of those proven winners - Tony Adams - relays an enlightening story about Wenger's treatment of Lilian Thuram at Monaco. Despite the reputation the defender eventually forged, at first he offered up regular errors.
"It cost them game after game. But he kept him on... and encouraged him and encouraged him. Great for the player. No good for [Wenger] and the team."
History has clearly repeated itself.
But not in every sense. Sunday's match at Old Trafford is likely to be a far cry from the testosterone-fuelled face-offs between men like Patrick Vieira and Roy Keane. Another difference, however, is that - on the evidence of the past seven years, let alone the last 10 months - only one of the teams is likely to reach the kind of level those forerunners once did.