Because it was David Luiz, everybody laughed. Because it was Paris Saint-Germain, everybody sneered, just a little. And because it was Jose Mourinho, everybody had to stand back and admire, too, watching in wonderment at his alchemist's touch, turning the basest of materials into wads and wads of notes.
These were all understandable reactions to the fact someone had decided to spend 50 million pounds on a central defender as clearly and as abundantly flawed as Luiz, to make the Brazilian the costliest defensive player in history ostensibly as part of a master plan designed to win the Champions League. It was funny, and it was crazy.
Looking back, though, we should not have laughed or sneered, and after admiring Mourinho's handiwork, we should probably have examined the entire incident for a deeper meaning. Because there's one in there, if you know where to look.
It was quite easy to laugh, last week, too, when Arsene Wenger was discussing the scrap between Barcelona and Manchester United -- two of the three biggest clubs in the world -- over Thomas Vermaelen, the third-choice central defender for the team that finished fourth in the Premier League last season.
"He has a choice of two massive clubs," Wenger said. "That tells you that these clubs have looked everywhere, and [that] it is not easy to find a player like Thomas."
It's not easy to find a player like Thomas. Of course, a manager has to feed a player's ego and layer on the praise. And of course, Wenger was being nice to one of his charges, but this was pushing it.
It's not easy to find a player like Thomas? A substitute central defender, when you're Barcelona and Manchester United? It might not be easy, but it's not exactly solving Fermat's theorem. It sounded so funny at the time. In hindsight, it wasn't. In hindsight, it was a clue.
And then, this week, came the third, clinching piece of evidence: On Monday, Manchester City paid FC Porto 40 million euros for Eliaquim Mangala. Well, they paid Porto 30 million euros, with the rest of the fee split between the two companies who own some 44 percent of his economic rights.
That is the same Eliaquim Mangala who you will remember from his role of "unused substitute" in the French squad at this summer's World Cup. The same Eliaquim Mangala whose only experience thus far is in two of Europe's second-tier leagues -- Belgium and Portugal -- and who has just three caps for his international side. Suddenly, though, Eliaquim Mangala is the third-most-expensive defender in history.
There are two patterns here. It does not take much to identify them or to discern how they are linked.
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One, defenders are getting more expensive. Mangala and Luiz are just the tip of the iceberg. Barcelona paid 16 million pounds to meet Jeremy Mathieu's release clause at Valencia, despite the fact he is 30. Liverpool -- who had snubbed their nose, like everybody else, at signing Dejan Lovren for 8 million pounds from Lyon a couple of seasons ago -- gave Southampton 20 million pounds for him this summer.
Throw in full-backs and the pattern becomes even more pronounced: Luke Shaw is the most expensive teenager in the world; Marcos Rojo will cost Manchester United another 16 million pounds or so; Calum Chambers had played just 23 first-team games for Southampton when Arsenal offered the same amount to bring him to North London.
This is explained by pattern number two: Defenders are getting rarer. Or, rather, there is a shrinking pool of top-class centre-backs (full-backs are a rather different phenomenon; their role is changing and so too is the profile required of the players who are asked to fill it). It is this that makes Wenger correct when he suggests it is not easy to find a player like Thomas.
In England, it is often remarked that the national team is enduring a famine after the feast in the heart of their defence. Just a couple of years on from the era of John Terry, Rio Ferdinand, Ledley King, Jamie Carragher, Jonathan Woodgate (who, if it had not been for injury, would have been better than the lot) and the rest, now the only high-calibre central defender Roy Hodgson has available is Gary Cahill.
But England is not alone. Look at Italy, where successors to the generation of Fabio Cannavaro and Alessandro Nesta are -- apart from Giorgio Chiellini and Leonardo Bonucci -- thin on the ground. Look at the partnerships for the Netherlands and Argentina at the World Cup; Gerard Pique has lost form spectacularly for Spain, and Sergio Ramos remains an acquired taste; it is only, really, France and Brazil who could claim to have any sort of strength in depth there at all.
That is not to say there are no centre-backs, of course. There are some, and very good ones: Mats Hummels, Medhi Benatia, Vincent Kompany, Diego Godin and, the best of the lot, Thiago Silva. But there do not -- at the risk of sounding vaguely geriatric -- seem to be as many as once there were.
This has given those clubs that require defensive reinforcements a problem. Those that are at the elite level are either out of reach, having already been acquired by one of the game's superpowers, or, like Benatia, have an extraordinary price tag attached to them. That has driven up prices for those on the rung below them -- Lovren, Mangala, even Vermaelen -- and made players that were once overlooked valuable assets.
Those basic economics explain why defenders are getting more expensive. What it does not answer is why they seem to be getting consistently rarer.
Partly, it seems logical to suggest that scarcity is to do with the rule changes that have effectively killed off the defensive midfielder: what is rapidly becoming an outright ban on all forms of tackling, the incremental creep that is seeing football turn into a non-contact sport. It is not that academies have stopped producing defenders, or that players no longer want to play in defence; it is just that, with their principal weapon neutered, it is much harder for them to look good.
But partly, it is to do with the shifting nature of their role. There is an increasing tendency -- thanks in no small part to Marcelo Bielsa and Pep Guardiola -- to see a defender's primary job not as destruction but as the first act of creation. That is why Guardiola was keen to deploy Javier Mascherano as a centre-back; it is why Bielsa turned Javi Martinez from a midfield dynamo to the heartbeat of his back line.
This has had two effects. One, those pure defenders who are not quite so neat on the ball -- someone like Federico Fazio or Nicolas N'Koulou -- are judged ill-equipped to play at the top level, and so are overlooked. And two, it has made those that can do it extremely valuable.
That is why PSG were happy to pay so much for David Luiz. They are prepared to tolerate his lapses, simply because his ability to build the play more than compensates for it. We laughed, we sneered and we marvelled when they did it. But really, we should have seen it as a sign of things to come.
Rory Smith is a columnist for ESPN FC and The Times. Follow him on Twitter @RorySmithTimes.