Letting Dani Alves leave for Juventus in 2016 was one of the biggest mistakes Barcelona have ever made. Not replacing him with Joao Cancelo, though, was an even worse decision.
The Portuguese full-back was just 22 at the time but it was obvious after his first season in Spain with Valencia that he had the pace and skills to flourish in a side as adventurous as the Blaugrana's.
Indeed, Cesare Prandelli spent just three months in charge of Los Che at the tail end of 2016 and that was more than enough time for him to realise that Cancelo was a special player.
"It's clear that he can become a champion," the former Italy coach prophesised at the time. "He has unlimited potential and is not an ordinary wing-back. In many ways, he is unique.
"He pushes forward a lot, has great physical attributes and is technically very gifted. He dribbles like a forward and you sometimes find him stopping a ball in the opposing area with the ability of a striker.
"He's a boy who still needs to become a more complete player, but he has incredible talent."
So much talent that it is remarkable that Juve had such little competition for his services during the summer. In 2016, Barcelona had considered making a move for a player Martin Montoya described as having "Barca DNA" but this time around the Catalans were nowhere to be seen.
The full-back's agent, Jorge Mendes, pushed his client towards newly-promoted Premier League pet project Wolves but Cancelo quite rightly felt he was ready to play for a Champions League team.
Inter wanted him, too, as Cancelo had enjoyed a successful loan spell at San Siro last season, but the Nerazzurri simply couldn't afford to stump up the cash to make his stay in Milan permanent because of their struggles to meet UEFA's Financial Fair Play (FFP) requirements.
Juve took full advantage of Inter's financial restrictions, as well as the bizarre lack of interest among the rest of Europe's elite, to sign Cancelo with the minimum of fuss for a bargain €40 million (£35m/$46m).
For a long time it seemed that, for fans and journalists alike, the most interesting aspect of Cancelo's transfer was that it had led to the arrival of his compatriot, Cristiano Ronaldo, in Turin.
"It all started with the deal for Cancelo, who has the same agent as Ronaldo, Mendes," former Juve CEO Beppe Marotta subsequently explained.
"When we realised that we could seize this opportunity, the shareholders agreed to support the club."
Thus, the wheels were set in motion on the biggest deal in Juve's history; it could well prove the best too, from both a sporting and commercial perspective.
After all, the Bianconeri's social media numbers have sky-rocketed, 'CR7' shirts are still flying off the shelves and the goals are flowing (10 in all competitions, including five assists).
But then, none of this is surprising. Juventus felt all along they were buying the best player in the world. What they did not know, though, was that, in Cancelo, they were also buying the best right-back on the planet.
That the 24-year-old was a player of enormous potential was beyond dispute. Juve had been watching closely as Cancelo made the entire right wing his own at the Giuseppe Meazza last season, as he helped Inter secure a return to the Champions League with a hard-fought fourth-placed finish in Serie A.
However, while there were no doubts over his many strengths from an offensive perspective during his temporary stay at San Siro, there were lingering concerns over his defensive work.
When he arrived at Juve during the summer, the feeling was that it would take time for Cancelo to learn when to bomb forward and when to hold back, just as it had with his equally attack-minded team-mate Alex Sandro.
The Brazilian had to study Patrice Evra's defensive movements during his first season in Turin before really establishing himself as a world-class full-back in his second term. Cancelo, though, is already ahead of schedule in that regard.
Offensively, he has been predictably excellent for Juve. Only Federico Chiesa has completed more dribbles than Cancelo (28) in Serie A this season, while he has 33 in all competitions. By way of contrast, Bayern Munich right-back Joshua Kimmich has 15 - despite having played seven more games.
Furthermore, Cancelo also ranks third among Serie A defenders in terms of chances created (17) and fifth for successful crosses (12).
However, what is most noticeable about Cancelo this term is the way in which he has improved defensively, both in terms of his positioning and his reading of the game, as illustrated by the fact that he has already made 74 recoveries – just seven less than Napoli's colossus of a centre-half, Kalidou Koulibaly, and in three fewer outings.
Cancelo was simply not as diligent last season, even if Juventus coach Massimiliano Allegri is reluctant to be drawn into making either comparisons or grand statements about his summer signing.
"I don’t know about last year,” Allegri told JTV after Cancelo had played a starring role in Juve's Champions League win over Valencia on matchday one.
"I know that this year he’s already improved a bit, but he still needs to improve because he has extraordinary qualities.
"He's still missing a little something to be the best in the world."
Allegri is now in the minority there, though. After a typically barnstorming display against Udinese last month, former Italy centre-half Daniele Adana could barely contain his excitement at what he had just seen.
“Cancelo is the best right-back in the world right now!" he declared. "For Allegri, he is like an added winger!
"He speaks the language of the number ones and he raises the level of Juventus among the top four-to-five teams in Europe." Just like Ronaldo, essentially.
Cancelo may not be drawing as many plaudits as his compatriot, but he is proving just as influential – and for roughly a third of the price.
Barca have yet to find an adequate replacement for Dani Alves but Juventus already have.