One is that arguably the most thrilling, exciting sight at a game is a punch-up. When fists start swinging, commentators quickly tell us that "no one wants to see this kind of thing", when in fact the opposite is palpably true.
Fans in the stands and watching at home love it when players lose their rag. To pretend otherwise is laughable, yet pundits feel obliged to act as our moral arbiters and tell us we shouldn't be enjoying an eruption of raw emotion.
Similar restrictions apply to managers and players, who, having won a first leg by a clear five or six, are apparently contractually obliged to state "there's still a long way to go yet" and "anything can happen in football", when, statistically, it can't. The tie is dead.
This - in a horribly roundabout way for which ED apologises - brings us to Chelsea's progression to the semi-finals of the Champions League, and another unspoken truth: that of the concept of revenge.
Revenge - like monogamy - is a dirty word in professional football.
It is a concept that journalists are obsessed by as it gives us an easy angle to pursue: what could be simpler than a direct line of cause and effect? "They want to do this because the other lot did that." Six hundred words filed, job done, and then it's off to the pub for a liquid brunch.
This is the reason why managers the length and breadth of the land are repeatedly assailed by enquiries as to whether an upcoming clash represents a chance to gain revenge for an event or result in the past; an injustice or an embarrassment.
The stock answer is something along the lines of: "that's in the past now, we move on and think about the game ahead of us."
But, though it can at times be an oversimplification of a more complex issue, revenge is a motivating factor for players. They won't often admit it in advance, as it leaves them open to accusations of being psychologically compromised and unfocused, but it is there.
At its extreme, this was demonstrated in Diego Maradona's analysis of his Hand of God moment: "We blamed the English players for everything that happened, for all the suffering of the Argentine people ... Before the match we said football had nothing to do with the Malvinas war. But we knew a lot of Argentine kids died, shot down like little birds. This was revenge."
Perhaps that isn't the best example for ED to be using, what with it being the 30 th anniversary of that certain war, but the point certainly holds: revenge is at times a motivating factor, whatever players may say publicly.
And with Barcelona awaiting in the last four of the Champions League again after Chelsea's win over Benfica, how could anything but revenge be on the minds of Roberto Di Matteo's players?
The Chelsea boss even admitted last night: "We have faced them a lot of times over the years and a lot of our players have some history against Barcelona. Certainly they feel a bit hard done by from when we played against them three years ago."
As many as eight of the starting XI from that controversial night at Stamford Bridge in 2009 - when Chelsea were denied a succession of stonewall penalties and were eliminated by Andres Iniesta's late goal - could be facing the Spanish champions again.
That infamous night when Tom Henning Ovrebo became the most hated Norwegian arrival in England since the Vikings razed the north. When Michael Ballack pursued the match official rather too physically and Didier Drogba chased after him in flip-flops and told the watching world "It's a f*****g disgrace!"
In fairness, it was rather, even if Drogba's behaviour was disgraceful itself and shamed his club (ED will never forget those inexcusable flip-flops).
If you can recall the days before Barcelona swept most sides aside with contemptuous ease - back when the Daily Mail mocked Xavi for being a bit rubbish, rather than the galactic overlord of possession that he is today - Chelsea had outplayed the Catalans and deserved to go through, only to be denied by some terrible officiating.
For a club owned by a man who is believed to covet the Champions League almost as much as he covets signing multi-million pound strikers who don't fit into his team's system, injustice on such a stage cut so, so deep, especially coming 12 months after John Terry's slip in Moscow and with Manchester United awaiting in the final again.
The wounds from that night are still red raw, and the upcoming semi-final represents the chance to right the wrongs of history and expunge from Chelsea's memory one of the most traumatic evenings in their history. Revenge is definitely in the air.
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This is all very well and good, but as for Chelsea's actual chances of enjoying revenge, they appear prohibitively thin.
Chelsea have regressed alarmingly since 2009 - whatever players may say about the impact 'Robbie' has had of late - while Barcelona have flourished and evolved under Pep Guardiola.
ED hardly needs to give you a rundown of what makes Barcelona the best team around - tiki-taka, Messi, Pep's skinny ties etc, etc - while Chelsea's own shortcomings are also rather evident.
Benfica coach Jorge Jesus felt sufficiently emboldened to say last night: "Chelsea have no chance against Barcelona", while Jose Mourinho, a man whose passion for the club is undoubted, said following Real Madrid's aggregate win over APOEL: "Barcelona aren't the favourites, they are super-favourites. Let me be honest, I don't think the final will be a Real Madrid/Chelsea final. It could be Bayern or Barcelona, I just don't think it will be Real Madrid v Chelsea and we know why."
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QUOTE OF THE DAY: "Negativity has been very much in the forefront recently, which is strange because we have lost one in 12. You get opinions about our results like 'James Tomkins shouldn't be playing in midfield because he is a centre-half.' You get all that b******s. What happens is I look at the performance of every player and say to everyone who says that: 'You're talking b******s.' He played in that holding role for three games when we had 10 men — so that is how short memories are. That is how much b******s is talked in football. I don't listen to that drivel because what bothers me is that James Tomkins plays well." - Sam Allardyce's war of words with West Ham fans intensifies.
FOREIGN VIEW: A French court has dismissed David Ginola's lawsuit for slander and defamation against former France coach Gerard Houllier after a 19-year feud between the pair.
Houllier's lawyer Jean-Claude Guidicelli said on Wednesday the court had ruled there were "irregularities" in the former Tottenham and Newcastle United player's case. "The court wanted to end this story by dismissing David Ginola's case," he said.
France failed to qualify for the 1994 World Cup finals when they lost 2-1 at home to Bulgaria after Emil Kostadinov's last-gasp winner in their final qualifying game. Houllier blamed winger Ginola for misplacing a cross that allowed Bulgaria to launch a decisive counter-attack.
COMING UP: It's the turn of the Europa League tonight with the four quarter-finals set to be resolved. All games kick off at 8.05pm and we have live text commentary on Valencia v AZ Alkmaar, Athletic Bilbao v Schalke, Metalist Kharkiv v Sporting and Hannover v Atletico Madrid.
Michael Cox, of Zonal Marking fame, examines QPR's attacking strategy against Arsenal at the weekend while the Armchair Pundit files his latest column. We will also hear from former Sheffield Wednesday and Burnley manager Brian Laws on his sporting heroes, while the Fantasist delivers his latest fantasy injury report and Never Mind the Ballacks report on events in the Bundesliga.