Louis van Gaal sat his Barcelona players down in the Camp Nou dressing room before what would prove to be the most heated clasico in memory.
"The team who will win will be the team who will control their emotions," he said.
It was October 21, 2000, and emotions were running high in Catalonia following the transfer of Barcelona's best player, Luis Figo, to Real Madrid.
"Van Gaal was right," recalls Luis Enrique, another Barcelona star. "How many times have we seen teams lose their heads and someone get sent off?
"I like the clasicos, the coach to the stadium. Even the warm-up was different ... because you didn't need one. You were already up for it. I could have started any clasicos without a stretch."
This particular occasion was most memorable for the moment a pig's head landed near Figo as he prepared to take a Madrid corner.
"But at that pig's head game," says Enrique, "I saw the Barca fans angrier than I've ever seen before. They're usually reserved. They go to Camp Nou to see a spectacle. The players said before: 'We're going to win this game. We have to win it.' It was strange that they only threw the pig's head; I thought they might throw the whole pig."
Barcelona duly won, yet while some had sympathy for Figo and his treatment, Barcelona's coach didn't.
"Figo provoked the situation," said Van Gaal. "He walked over to the corner slowly, picked up a bottle slowly, went back to the corner - and all this consciously and deliberately, without the referee doing anything to stop it."
Sentiment or sympathy is not something that the Dutchman specialises in and is something his new No.2, Ryan Giggs, will soon learn.
As well as Van Gaal, Enrique, who has now been appointed Barcelona manager for next season, played under Vicente del Bosque, Bobby Robson, Jorge Valdano, Leo Beenhakker, Serra Ferrer, Camacho and Javier Clemente.
"The trainer I learned most from about the field of play was Van Gaal, even though he's the one I've had the most confrontations with," says Enrique.
"Well, disagreements," he adds with a smile. "He's got an obsession with work ethic, the way he plans. Maybe I preferred a lighter style to his.
"You learn something from everyone, even the bad coaches. Because they tell you something, and you think: 'I'll never do that in the future.'"
Van Gaal has become the new manager of Manchester United and he has shown before that he is adaptable too. When he took over from Robson at Barcelona in 1997, on a mission to make the club play like his Ajax team that had won the European Cup two years earlier, he inherited an assistant named Jose Mourinho.
Robson could have been angered at his departure, but he encouraged Mourinho to stay on with his replacement and even recommended him.
Van Gaal discovered "an arrogant young man who didn't respect authority that much, but I did like that of him. He was not submissive; he used to contradict me when I was in the wrong. Finally, I wanted to hear what he had to say and ended up listening to him more than any of the assistants."
Van Gaal promoted Mourinho and trusted him to scout big-game opponents. He also placed him in the stands rather than on the bench for a different perspective. Mourinho would report to him at the start of half-time, and Van Gaal would relay this to the team. The manager saw talent and trusted his assistant. He was right, but the two would argue.
"Mourinho wanted to know everything that was going on, not just with the coaching," former Barcelona defender Michael Reiziger told me. "The players liked that. I'm not sure Van Gaal always did, as they both wanted to speak the most. So he wasn't a normal assistant. It was clear that he wanted 'something else.'"
Mourinho learned. "With Van Gaal," he said, "the practice sessions were set out already. I would know everything beforehand that we were going to do in training. From the aims, to the exact time each exercise was going to take place. Nothing was left to chance, everything was programmed to fine detail."
But he tired of working under the Dutchman. Van Gaal's downfall was that he failed to lift the Champions League in two spells at Barcelona.
Fans had hoped to do it in 1999, the club's centenary year, in the final at Camp Nou, but a team of red-shirted heroes earning their living in the northwest of England had other ideas.
Several of those players were put in charge at United for the final four games of the season following the sacking of David Moyes. Van Gaal has chosen one of them, Giggs, to become his assistant manager and the way their relationship develops will be fascinating.
Van Gaal delivered the league title in each of his first two seasons at Barcelona, but unfavourable comparisons with the football played by Johan Cruyff's 'Dream Team' didn't help his case.
Nor did his confrontational public demeanour in front of journalists, or the fact that he virtually transplanted the Dutch national side (of which he is the current manager until after the World Cup) to Catalonia.
It's important to Barcelona fans that Catalans represent their club. They welcome foreigners, but the balance that Cruyff had managed was not maintained by Van Gaal. Critics questioned the "Hollandisation" of the club and debated the merits of why so many of Europe's great underachievers were being transplanted to Catalonia.
When he was brought back for a second spell at Barcelona in 2002, the decision was derided, even though Van Gaal promised that he had changed.
For all of a week, he did seem relaxed, shaking hands and kissing babies in public, only to return to his usual confrontational self when his team faltered immediately in the league.
Salvation could have come with the re-signing of Ronaldo, offered to the club by Internazionale, but Van Gaal declined. The Brazilian went to Real Madrid and started scoring freely. Van Gaal lasted six months.
Yet this is a man who gave a debut to Xavi in a Champions League game at Old Trafford.
"It was so intense," Xavi says. "Imagine what it was like for me? I was 18 and had been playing for Barca B. I'd not even played for the first team. I was still getting the metro to training, and there are 50,000 crazy Englishmen screaming in my ear."
Xavi has since gone on to make more appearances for Barçelona than any player in the club's history. Like Giggs at United, he has become a decorated club legend admired by the football world. Unlike the Welshman, he has not yet been afforded the chance to learn from the Dutchman as his No.2.
Manchester-born Andy Mitten founded United We Stand in 1989, aged 15. He has written 11 books since his career began in 1995 and visited almost 100 countries while working for numerous magazines and newspapers worldwide. Follow him on Twitter @AndyMitten