Such has been Zinedine Zidane's "Midas" touch since taking over at Real Madrid in January 2016 that any club wishing to wrest La Liga or the Champions League will need to have a coach who wins one-vs.-one battles with the Frenchman -- before and during matches.
That goes for Diego Simeone, Jose Mourinho, Pep Guardiola, Antonio Conte, Unai Emery and, particularly, Ernesto Valverde because they comprise the only other managers, whose teams I can conceive of conquering Europe this season (Simeone and Valverde are also required to keep pace with Zidane domestically).
It's a hot subject and not simply because the reigning Spanish, European and world champion manager has repeatedly made brave, visionary, common-sense and knowledgeable calls, which have paid off over the course of his astonishingly successful reign.
At the weekend there was a like-for-like comparison between Valverde and Zidane. What we learned was that the Barca boss has a great deal to do in order to close the gap between him and his Madrid counterpart; perhaps not surprising given that Valverde has had less time in the job and, frankly, has a bigger job on his hands.
While he won kudos and respect for the terrific way he handled adversity in a 2-1 win against Getafe, the thing that will concern Blaugrana watchers is that some of the difficulties faced were caused by his own decisions.
Meanwhile, as the top half of La Liga waited anxiously to see whether a visit to Real Sociedad would extend Madrid's slow start to the season, Zidane pulled off a couple of masterstrokes that helped tuck three restorative points in the bag, long before Gareth Bale scored his fabulous goal to make it 3-1 to the reigning champions.
Barcelona's visit to Getafe always presented as a match in which industry, energy and sheer work rate would be needed from a classier side to subdue an ebullient team that still feels top of the class, having secured promotion with such assurance at the first time of asking (Saturday was their first home defeat in a year).
Valverde talked about a "nine-point week" and intimated that his squad rotation would be based on the fact that Barcelona's following two matches, at home to Eibar on Tuesday and then in Girona four days later, were equally vital and would come with a "bang-bang-bang" rhythm, hard on the heels of what had gone before.
Then he shocked everyone by keeping 10 of the same 11 players, who started against Juventus in midweek; moreover, nine of those also began against Espanyol the previous Saturday.
The visit to Getafe offered Valverde the chance to cash in on the fact that he's weaned Andre Gomes, Paulinho and Gerard Deulofeu into the season and to give Denis Suarez, Javier Mascherano, Lucas Digne and Aleix Vidal merited minutes. Not all of them would start, but perhaps three or four of them would get a chance.
Here's the logic. First, one of the flaws of Barcelona last season was that they often looked athletically challenged: Teams outran them, outworked them and outmuscled them.
Valverde has addressed that to the extent that everyone is pressing, everyone is supporting each other and the laissez-faire of the last 12 months has been replaced by a hard-nosed, blue-collar, sleeves-rolled-up mentality. But it comes at a cost: It's mentally and physically draining.
Long before a ball was kicked on Saturday it was obvious that Andres Iniesta might yield benefit from starting on the bench. Last season his game time was limited by a series of injuries but, so far, in 2017-18, he's looked happy, effective and rejuvenated.
But he's 33 years old. This was a test where sharpness, running and tackling were initially going to carry a high premium and where Iniesta coming into the fray, when the game was more open and Getafe were weary, looked logical.
He's played over 500 competitive minutes this season -- more than one third of his Liga total last season and we're only in September -- and, moreover, his games have been properly testing: Real Madrid in the Super Cup, Juventus in the Champions League, the Catalan derbi, and Spain vs. Italy.
Equally, Iniesta, Lionel Messi, Luis Suarez, Sergio Busquets, Ivan Rakitic, Jordi Alba, Gerard Pique and Samuel Umtiti have all recently played significant World Cup qualifiers, followed by the adrenalin rush of facing city rivals Espanyol and Juventus. Thus the idea of a drop-off in the next game, away in mid-afternoon to Getafe, was very predictable.
Also absolutely vital for any top squad is that the so-called first XI feel the breath down their neck of the guys who want to take their jobs. Competition for starting places must be shown to be a meritocracy, something Zidane has managed to achieve at Madrid. It makes everyone's attitude keener, harder and more durable.
Valverde, though, must have thought of his veteran line-up: "This XI is in form, these are my go-to guys, I'll reward the senior players who want to start every match by sticking with them."
Think again, Ernesto.
Did playing Ousmane Dembele again, days after an examination of his fitness against Juve and following a disrupted preseason in which he forced a move to the Camp Nou ahead of focusing on his fitness, contribute to the excruciating injury he suffered?
We'll never know that for sure, but what was clear was that the sloppy nature of Barcelona's first 50 minutes or so indicated Valverde erred in not rotating his squad.
Physically they were second best and, mentally, they were full of cobwebs: Passes were misplaced, wrong options were taken and there was insufficient competition for loose balls.
And when changes were made, the three most obvious candidates to be rotated -- Dembele, Iniesta and Rakitic -- were the three players who were replaced. That tells its own story.
As mentioned, Valverde deserves kudos for getting both key changes -- Denis and Paulinho came on and scored -- spot-on. In real terms, the decisions maintained Barcelona's four-point lead over Madrid. But his self-correction stemmed from an avoidable error.
"You can't get through the whole season with just 11 players; you have to make changes," he admitted on Monday. "Some people say that you can only rotate players when you are losing. When should rotations be made? That's something that you have to work out."
And quickly, I'd suggest.
Meanwhile, Zidane deserves greater kudos, again.
Having dropped four points dropped in sequential home league games and played a listless first half against APOEL in the Champions League, Madrid faced a visit to co-leaders Real Sociedad without Karim Benzema, Cristiano Ronaldo, Marcelo, Toni Kroos and Mateo Kovacic. Not ideal.
It looked like a clear case for packing the midfield, pushing Bale and Marco Asensio up front and using a 4-4-2 formation to play on the counter-attack. Instead Zidane trusted Borja Mayoral and won dividends that weren't simply to do with the two goals the 20-year-old either scored or provoked.
The use of a centre-forward, who hadn't scored since last February and who had not started a competitive match since returning from his loan at Bundesliga side Wolfsburg, meant that Asensio and Bale played wide on the left and right respectively.
The idea was to try and stop La Real's rampaging full-backs Alvaro Odriozola and Kevin Rodrigues from doing the kind of damage that they, along with Alberto De La Bella, have inflicted already this season.
The result was that Madrid flooded the final third and La Real were often pinned back. While both Rodrigues and Odriazola did some damage, imagine what might have happened if they'd been allowed to push into midfield and give Eusebio Sacristan's team superiority of numbers there or, worse still, up front?
You'd be lying if you don't admit that, not so long ago, the idea of playing 4-3-3 at home was regarded as daring. To do it away from home would have been called cavalier to the extent of being deluded. But Zidane made it work and. Further, the trust he placed in Borja was paid back in spades. It's the equivalent of Valverde placing huge responsibility on the shoulders of, say Paco Alcacer, Carles Aleña or Andre Gomes.
Madrid's coach has, without question, proved to be a player-whisperer and there isn't a single footballer, with the possible exception of Fabio Coentrao, who hasn't improved under Zidane's first-team tutelage.
Which is why I pay off this argument with Bale. Zidane has demanded that the media agenda change and that the squad start to give Bale a "we love you, big guy" vote of confidence. He's tried to inject a sense of self-belief in the woebegone Welshman. There has been a one-man campaign in Bale's favour and it's come from his boss.
Zidane needs Bale, whose power, pace, goals, aerial ability and sublime assist-giving ability off his left foot will be vital this season in the absence of Alvaro Morata and James Rodriquez.
And so, in private and in public, Zidane has been building up the footballing well-being of Bale who, though built like an elite super-middleweight boxer, has a psyche that is as prone to doubts and worries as is yours or mine.
Last Friday, two days after Bale created all three of Real Madrid's goals against APOEL, Zidane said he still had a couple of months leeway, because of his injury absence last season, before he could be expected to be at his absolute best.
On Sunday, Bale played discretely but kept his confidence, kept working and scored one of his best goals for months, latching on to Isco's quarterback pass to outrun La Real's defence and finish deftly.
Zidane was a god of football, blessed with balance, grace, technique, power and vision. But he also possessed a streetfighter's instinct that led to numerous red-card incidents, including perhaps the most famous in history at the 2006 World Cup, characteristics that distracted attention from his wisdom.
He watches, draws good conclusions and makes good decisions. It all means that his rival managers must not only ensure their squad and team are as good as Real Madrid, but also that they must operate on Zidane's level if they are to prevail.