There are a number of reasons that footballing theories become cliches, but foremost amongst them is that they are true.
On Tuesday night, Tottenham Hotspur proved two such well-worn opinions: namely, Premier League sides are full of energy and vigour, whilst Italian teams are slow and cluttered with old players.
Spurs completed one of the most memorable nights in their history by winning 1-0 against AC Milan in the San Siro and are strong favourites to go through to the quarterfinals. In doing so, they underlined their status as one of Europe's up-and-coming forces.
Maybe they will pass AC Milan on the way down.
Tottenham's starting team had an average age of exactly 27, with only two players over 30. AC Milan's, meanwhile, had an average age of 29.9 and five players the wrong side of three decades. It showed.
Spurs opened full of vibrancy and pace, taking the initiative in the starting exchanges and playing the role of the home side with such conviction that the Milan players must have believed it. The Rossoneri were woeful in the first half, playing with all the youth and style of Tony Blackburn.
It had to get better in the second half for Milan. It couldn't have become much worse. But it did.
Their performance did improve, largely due to the introduction of Pato, who added some much-needed impetus to a front line lacking ambition and ideas. Their discipline, however, disintegrated into the storm blowing through the San Siro.
Flamini first lunged two-footed into Vedran Corluka in an atrocious challenge which saw the Croatian leave the pitch, emerging in the dug-out on crutches and in an ankle brace.
This wasn't the end, though. Oh, no. Gennaro Gattuso saw to that.
In a flurry of elbows, pushes, dissent and vicious tackles, "The Growler" was lucky to still be on the pitch by the full-time whistle—at which point he proceeded to headbutt Joe Jordan, Tottenham's assistant manager.
Previously in the game, Gattuso had shoved Jordan in the throat after an altercation.
Gattuso, unsurprisingly, picked up a booking in the second half and so would have missed the second leg anyway, but UEFA will surely be looking at his behaviour after the match and he could well be on the receiving end of a hefty ban. You won't see many Spurs fans arguing if he does.
As the game descended into a large-scale brawl at the end, AC Milan only served to justify another cliche in football: Italian clubs are prone to ill discipline.
A team top of their domestic league and with seven European Cups to their name might have been expected to show a touch more class in the continent's premier competition.
As it was, all the class belonged to Tottenham - a team who could be replacing them at Europe's top table.
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