A glance towards Saturday's results from all around Europe frequently show hangovers from those who have been involved in midweek exertions.
It happened to Celtic on Saturday, yet what rankled with Neil Lennon was not the result but the manner in which his young Hoops side allowed Hibernian to wriggle out of Parkhead with a point.
At half-time, you would have put money on Celtic bagging at least four or five. Instead, they fell asleep, allowing their Edinburgh visitors cheap goals and an unexpected point.
In the grand scheme of things, it will probably matter very little.
Celtic should not have to peer over their shoulder this season due to the unusual set of circumstances that Scottish football finds itself in, but at the same time there was an ire and an exasperation from Lennon throughout the contest as he grew more animated on the touchline.
When Mikael Lustig and Fraser Forster messed up an anodyne Hibs opportunity to give Pat Fenlon's side a way back into the game, the Celtic manager was fuming.
Goalkeeping coach Stevie Woods, positioned somewhat unfortunately behind him, was quick to get it in the neck.
Yet, for all that Lennon's blood pressure soared in tandem with the bucketful of errors that his youngsters made during the game, by the time the whistle had gone and he spoke to the media, he had cooled off.
However, with a fresh test away from the SPL on the horizon, it is unlikely he will be prepared to forget Saturday in a hurry.
With the Uefa Champions League looming and games against Barcelona, Spartak Moscow and Benfica coming up, he will want an edge to his side. Lennon will want to see Fortser and Lustig commanding rather than dithering, he will want to see Filip Twardzik know where he should be positionally and he will want to see chances converted rather than squandered.
Had that happened against Hibs, the visitors wouldn't have had a hope at coming back in the game.
Celtic will point to the woodwork twice denying them, but there was also a hole as obvious as a missing front tooth that opened up when Victor Wanyama went off with a dead leg.
The midfield powerhouse has only just turned 21. He is not that much older than Twardzik or Tony Watt, yet his significance to Celtic is difficult to overstate.
The club has put a £10million pricetag on his head and were quick to rebuff a £6m offer from QPR last week, and it is not hard to see why.
It isn't coincidental that in his absence Hibs suddenly found a lifeline, although shocking mistakes at the back played as big a part.
But the Easter Road side were allowed to come from behind not just once, but twice at Parkhead.
Sloppy habits can start to become entrenched, especially in a domestic season as odd as this one.
So to stop any repeats of Saturday's bloopers, it may mean that throwing in so many young players simultaneously won't happen too often.
Lennon was virtually without his senior midfield on Saturday, with the exception of Forrest, who was once again excellent.
Scott Brown, Joe Ledley, Charlie Mulgrew, Beram Kayal and Georgios Samaras were all injured, while Wanyama couldn't last the game, meaning that there was a real shortage of experience throughout the team.
Teenage striker Watt has hit the headlines in the past week for his performances, but he missed a one-on-one chance and his head went down a little bit afterwards.
"Tony has had a sensational few days, but he came back down to earth on Saturday," said Lennon.
"He was a bit flustered and lost a wee bit of composure, but you know you are going to get fluctuation with young players.
"It's a good opportunity to blood the kids, but they have got to grow up quickly. We might not be able to have so many of them in the side at the one time and it was a young team that we had out there."
Despite his irritation at the mistakes, Lennon was philosophical afterwards. And nor was he in the mood to single out anyone.
"I'm not disappointed at all, but I am annoyed at the two goals that we conceded because they were poor," he said.
"I don't want to blame anyone – that is for the confines of the dressing room – but the players were left in no uncertain terms about what is expected of them. We were a little bit light, but we should have won the game.
"Forrest was excellent. I run out of superlatives for that boy. I also thought Gary Hooper played very well and in an attacking sense Lustig was excellent and Kelvin Wilson did well again too.
"We're lacking a wee bit of experience and if you concede goals as poorly as we did sometimes you won't win."
It is difficult to imagine Lennon accepting many repeats this season.