It's no secret that Pep Guardiola keeps one of Marcelo Bielsa's speeches in his office.
The Manchester City boss has a script of the Argentine talking about failure on hand to help him cope with some of his tougher days in management.
Throughout his spells in South America and Europe, with a brief period spent in Central America, the Leeds boss has proven hugely influential in the careers of some of the world's best coaches, including Guardiola, Diego Simeone and Mauricio Pochettino.
In many ways, English football is blessed to be experiencing the eccentricities of 'El Loco', but his admission that his side have been spying on all of their Championship opponents this season has prompted fierce debate about the spirit of the game.
Far from apologising, the 63-year-old used his Wednesday press conference to showcase, PowerPoint and all, exactly how much detail he had compiled in his dossiers on each team.
As he explained, this is a tactic he has always used - it's just never attracted as much fuss as when his employees were caught out at the Derby training ground.
In fact, back in his La Liga days, he attempted to get the better of Pep Guardiola by compiling a huge document full of information on Barcelona's tactics, formation, and possible line-up - though it didn't pay off on that occasion.
"When I was a coach of Athletic Bilbao we played Barcelona in [the Copa del Rey] final and we lost 3-0," Bielsa told reporters, quoted via FourFourTwo.
"[After the match] I gave all the information I had on Barcelona to Pep Guardiola.
"Guardiola had a look at it and he told me 'you know more about Barcelona than me!'.
"I do this analysis to ease my anxiety, but it was useless information because they scored three goals."
As it turned out, Guardiola had nothing to fear.
And his reaction said it all. Bielsa and his staff genuinely invest up to 300 hours in studying every side his team come up against - it's absolutely insane.
There's another school of thought, incidentally popular with one of his disciples, Pochettino, that says managers are better off ignoring how the opposition are going to set up and focusing on their own game.
Tell that to Bielsa. In most cases, it must make a huge difference - there was just no way that Bilbao XI was going to beat Barcelona in a cup final.
Is what Bielsa has done wrong? Have your say in the comments.