We look for meaning -- especially these days -- and there was plenty to be had in an empty Camp Nou. Kylian Mbappe's hat trick -- only the second Barca conceded at home in the Champions League after Dynamo Kiev's Andriy Shevchenko in 1997 -- propelled Paris Saint-Germain past Barcelona 4-1 and, to some, it will symbolise him taking the baton from Lionel Messi.

That's nonsense. That's premature. Not just because Messi is Messi (and because that other guy in Turin might have something to say about this) but because Mbappe is writing his own history, one not defined by others. With Neymar (and Angel Di Maria) absent, he he guided PSG with the calm of a veteran, the exuberance of a kid and, above all, a rare blend of talent, athleticism and intelligence.

The image of him after the fourth goal -- arms open like Rio de Janeiro's Cristo Redentor, head nodding like a bobble-headed doll -- encapsulates just what he brings. That's meaning enough. The next decade belongs to him.

As for Barca, the night reaffirmed just how deep the rebuild ahead will need to be. There will be no Champions League band-aid to paper over cracks (and, perhaps, less Champions League revenue than anticipated), the seven straight La Liga victories mean little. This is a team that has been emotionally razed to the ground. They'll be back, building around Marc-Andre ter Stegen, Ansu Fati, Pedri, Frenkie de Jong (though maybe not Wednesday night's version) and possibly one or two others. Messi? We just don't know and won't for a while. But the boil had to be lanced and it happened against PSG.

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For many of Europe's super clubs, the Champions League knockout rounds are an early ritual of spring renewal. It's a chance to forget whatever woes afflict you domestically and relaunch your season. Both clubs had plenty of woes to consign to the past.

PSG, last year's beaten finalists, are embroiled in a legitimate three-way dogfight for Le Championnat with Lille and Lyon. It's not a role to which they're accustomed, given they've won seven of the past eight French league titles. But even beyond that, things have been far from comfortable at the Parc des Princes. They parted ways with manager Thomas Tuchel on Christmas Eve and have been fretting over things like Mbappe's new contract and Neymar's beach-house festivities.

Of course, that was positively halcyon compared to Barcelona's past six months. From Messi's Burofax to president Josep Maria Bartomeu's resignation to dire warnings of insolvency and financial meltdown to a freakish run of injuries that robbed them of Gerard Pique (the "other" resident icon and Mr. Shakira), Fati (the heir apparent wunderkind) and jack-of-all-trades Sergi Roberto, it's been a campaign to forget. And that's before you get into events domestically that, thus far, see them third in La LIga, eight points behind Atletico Madrid (who have played one fewer game).

Escaping from all of this was motivation enough, even before last week's "Affaire Messi," when the esteemed French magazine France Football put the Barca star -- who becomes a free agent in 134 days -- on its cover with a photoshopped PSG kit, prompting gnashing of teeth and pulling of hair back in Catalunya.

It's easy to forget that, for all the glamour and bon vivant imagery set against the backdrop of the City of Lights, there's plenty that's genuinely blue-collar about this PSG side. For every social media sensation that rocked up with a ready-made entourage and nine-figure transfer fee (read: Neymar and Mbappe), there are plenty of kids, grinders and second-chancers too.

Moise Kean and Idrissa Gueye arrived from -- with all due respect -- Everton. Marco Verratti landed as a teenager after a season in the Italian second division. Keylor Navas came after losing the starting job at Real Madrid. Alessandro Florenzi is on loan from AS Roma, where he was unwanted. Layvin Kurzawa has been at the club for five years and never started as many 20 league games. Leandro Paredes was a bust in Italy before reinventing himself, to a point, in Russia.

Mbappe would go on to take the headlines and rightly so. Not just for his hat trick, but for the leadership and precocious savvy he shows at 22 years of age, particularly with his favoured sidekick, Neymar, absent. But there was a lot of the supporting cast in his victory, plenty of "we're your foot soldiers, lead us to the promised land." That they would put so much of their trust speaks volumes: they know him best, they know what he offers.

Across the way, Messi has carried Barcelona for most of the past 15 years. And he had begun 2021 on a high, with nine goals in ten games, all of them from open play. When he nonchalantly stroked it on a dime to De Jong from deep, it led to Kurzawa conceding a soft penalty, which Messi himself converted. Less than half an hour had gone. He turned wordlessly to his teammates, his hooded eyes saying, "I got this."

Just like he had so many times in the past.

But he didn't. Because with this Barcelona team, whenever the Messi ticker shifts from superhuman to merely outstanding, bad things are wont to happen. And PSG's riposte was near immediate. A brilliant pass from Verratti, a first-time low cross, a somewhat lucky control that froze Clement Lenglet and Mbappe had rifled the ball into the back of Ter Stegen's net. Quick feet, quick mind, quick turnaround.

Moments later, Kurzawa again got away from Ousmane Dembele and forced Ter Stegen to make a world-class stop. Pique, who had willed his 34-year-old body back into the starting lineup after a nearly three-month layoff, waved his arms and pleaded with his teammate. But there was a sense of foreshadowing for what would happen in the second half.

Barca boss Ronald Koeman spent much of the time haranguing his back line, ordering them to defend higher up the pitch and let Ter Stegen worry about the ball over the top. But when you play with fear and little confidence and weary legs, you get sucked back towards your own goal. And it's not a coincidence that at the half it was PSG who had the bulk of possession.

Ter Stegen again had to perform a minor miracle at the start of the second half after a driving Mbappe run -- there's plenty of horsepower under that hood -- and 20 minutes later PSG were in the lead. Paredes found Florenzi, Pique botched his clearance and the ball fell for Mbappe to make it 2-1. And, before Barca realised it, it was 3-1, with Kean somehow making himself invisible between Lenglet and De Jong to beat Ter Stegen.

By this point, the blow was as much psychological as it was physical and practical. Mbappe, on the break, made it four, which matters because a PSG defeat by four clear goals at the Parc des Princes -- which is, realistically, what it would take for them to go out -- appears about as likely as Cristiano Ronaldo replacing Messi at the Camp Nou next season.