They say a trip to play Celtic is a vital part of your footballing education.
And, of course, when I say they, I mean some of the greatest to ever play the game.
Barcelona's Xavi: "The atmosphere generated by the fans in Celtic's stadium for our visit was the most impressive I've ever witnessed. The grounds of Liverpool and Manchester United are good and the hostile feeling of playing against Real Madrid in the Bernabeu is also excellent, but the atmosphere against Celtic was the best."
If the opinion of Xavi is not enough, how about someone equally as brilliant and smart. Someone like Paolo Maldini...
"Every professional footballer should seek to play at least one game at Celtic Park. I have never felt anything like it," he said.
The great thing about Maldini and Xavi is that they are all-time greats, not only for the way they played on the field but also for the way they carried themselves off it. They speak, you listen. They remain two of the smartest players I have ever watched and listened to. Throughout their long careers at the top of the game, they certainly never referred to themselves as one of the game's best players.
And then there is Mario Balotelli and the comments he made to the Scottish Sun newspaper this week: "I have heard all about the fans and the atmosphere they create - and my message to them is bring it on!
"If fans want to try and make a stadium hostile for me - or boo me because I am one of the best players in the world - then I hope they do."
One of the best players in the world, eh? Okay.
The Italian touched down in Glasgow this week having played a total of 27 Champions League games in his career. For his three teams, Inter Milan, Manchester City and AC Milan, he was important enough to only have started just 11 of those, coming on 16 times as a substitute.
He had scored just seven Champions League goals in 1,276 minutes played, averaging a goal every 182 minutes. For Inter, he was nothing more than an after-thought on their way to glory in 2010 while at City, he started just two of 12 matches, spread over two frustrating campaigns for both club and player.
The third chapter in his Champions League career is back at the San Siro. For now. The thing with Mario is, you just never quite know what he is going to do next, and that includes choosing where to play.
On Saturday, in a league game against Genoa, Balotelli missed a penalty in a frustrating 1-1 draw that sent the Italian giants down to 13th in Serie A.
After the match he took to twitter to thicken the plot.
Before the Genoa match, he had told the Italian press 'I am happy at Milan and I am happy to be here.'
Balotelli certainly played happy, despite making it eight straight games without a goal, and was a menace throughout the match and arguably Milan's best performer. That didn't stop Milan fans from voicing their complaints after the game towards Balotelli and his teammates.
It is hard to blame them. Their performances, just like their league position, have not been good enough. Yet, with the transfer window closed until January, this is not a club Balotelli can run away from.
At Inter and Manchester City, Balotelli was surrounded by a plethora of outstanding players who could easily demand a starting spot ahead of the Italian, who could happily move aside and away from having to perform on the field.
At Milan, things are very different. An out-of-form Balotelli, smiling or sulking, remains the club's best option up front. There will be no sitting on the bench for Mario.
And so with that presents the self-proclaimed 'one of the best players in the world' an opportunity, a run of games to help carry Milan back towards the top three in Serie A and into the last 16 of the Champions League.
"Great atmosphere always brings the best out of me," he had said in the run-up to the game and so it proved. The game was effectively over as a contest just after half-time, with Milan's both goals coming from corners that Celtic failed to deal with, killing the usual atmosphere Celtic Park is famed for.
Much will be made of Kaka's easy header inside the box to open the scoring but it was Balotelli's run from a deep position that led to a free kick that won the corner and placed Milan into scoring territory.
It was to be that kind of day for Balotelli, a day where he would have to bide his time, show patience and a mature side to his game when waiting to receive the ball. It is these kind of games that people have wondered about the 23-year-old. He is built very much like a striker who can play up top on his own, but his overall attitude and tendency to drift out of games is one of the reasons he hasn't started as many Champions League games as he should have. At Celtic, he had an appetite to come deep to receive the ball, start quick counter-attacks with his midfielders and drift wide to provide key outlets and pull the central defenders into areas they don't want to go.
Balotelli would get rewarded for his hard work when he scored his eighth career Champions League goal in the second half, coming deep, before timing a run superbly, sprinting into space to receive a great ball from Riccardo Montolivo and finishing it off at the near post. He also used his supreme strength to brush aside the defender, let the ball run, and not even touch it until he kicked it into the net.
He wasn't the best player on the pitch for Milan but on this night, he didn't need to be. The fantastic Kaka, playing behind Balotelli, was, as the Brazilian rolled back the years with a sensational performance that included powerful runs from distance, incisive passes and an ease at finding space.
Kaka, unfortunately, won't be given such space by many teams in Italy and so the responsibility of carrying Milan back towards respectability falls at the feet of Balotelli. In Glasgow, perhaps without even knowing or caring, he passed another test of his footballing education and finally showed signs that he does have an ability to lead the line for a team in Europe's elite club competition.
He is far from 'one of the world's best players' but if he wants to get anywhere near to the level once shown by Maldini, and still shown by Xavi, the European Champions League gives him the stage to perform.
We know how much he likes a stage, now it is up to him to ensure what he does on it.
'Why Always Me?'
The truth is it hasn't been about you enough, Mario.