It is nearly two months since Arsène Wenger discovered that Arsenal's season would begin with a difficult home match against Liverpool.

The Arsenal manager knew that he had players involved in Euro 2016 and he knew that, depending on how far their countries went in the tournament, some of these players might struggle to be available for the start of the season.

This last difficulty was self-imposed. Wenger has stated as a matter of principle that every player involved in an international tournament has to take a long holiday. “I believe that they need four weeks’ holiday,” he has said, “to regenerate . . . to recover completely, and they need to come back with hunger.”

Since Olivier Giroud and Laurent Koscielny played for France in the final of Euro 2016 on July 10th, they were therefore not allowed to return to training until August 10th – too soon, Wenger reckoned, to make the Liverpool game.

Every manager is aware of the importance of post-tournament rest but some of them bend the rules. José Mourinho also has a player who featured for France in the Euro 16 final. Anthony Martial played 85 minutes of Manchester United's 3-1 win over Bournemouth.

Training

Aaron Ramsey’s Euro 2016 ended just four days before France’s. Yet he returned to training a week earlier than the other two, played two pre-season matches, and was deemed fit enough to line out yesterday.

Of course, Ramsey didn’t actually play in Wales’ Euro semi-final due to suspension. So his last match was in the quarter-final against Belgium, nine days before the final. But the really hard thing about tournaments is surely not the football, it’s everything else – the psychological drain of being in an intense competitive bubble for several weeks. The fatigue is mental rather than physical.

It’s hard to see, then, how Euro 2016 was much less draining for Ramsey, who was part of such an epic campaign with Wales, than it was for Koscielny or Giroud.

But Wenger decided that Ramsey could play, while Koscielny couldn't. Since Per Mertesacker and Gabriel were injured, that meant that Arsenal started against Liverpool with a centre-back partnership of Callum Chambers and the 20-year old signing from Bolton, Rob Holding.

To recap: rather than ask Koscielny to come back a few days early, Wenger asked a 20-year old to make his debut in a crucial match against a close rival. “He has played in the Championship, so that is a good experience to deal with one level higher,” he explained.

Maybe Wenger thinks the Championship is full of players like Philippe Coutinho, Roberto Firmino and Sadio Mane. Liverpool lined up with no striker and a host of pacey internationals who surged into the box from deep; maybe Wenger imagines Holding played against teams like this every other week for Bolton.

Although Holding was not conspicuously at fault, you wonder what being part of a defence that was ripped apart on his debut will do for his confidence. And as Liverpool went 4-1 up, you wondered whether Koscielny would have traded a couple of days of holiday to be involved, rather than sitting in the stand in a suit.

As though to rub in the futility of Wenger’s planning by principle, Ramsey went off with an injured hamstring. The important point is that Wenger did not have a pressing need to play Ramsey – Alex Oxlade-Chamberlain could have played instead – whereas there was an obvious need for Koscielny. Wenger allowed principle to guide him, but managers also must know when to bend their principles to handle difficult situations.

Wenger's counterpart, Jurgen Klopp, saw his own faith in certain principles tested in the first half, as his left-back Alberto Moreno staged a one-man campaign to throw the game away.

Moreno’s last competitive match had been the Europa League final, where his mistakes cost two goals. It was expected that Klopp would replace him, but Liverpool still haven’t signed a new left-back.

Arsenal's first goal appeared to show everything that is wrong with Moreno. Moments earlier, Simon Mignolet had bailed him out by saving a Theo Walcott penalty that Moreno had given away with a characteristically bizarre foul. In the next move, Moreno won the ball and passed to Henderson. As Liverpool tried to counter, Moreno moved forward in support. But Lallana unexpectedly lost the ball to Coquelin, and Walcott scored through the space Moreno had left unguarded.

Terrible

Despite this horror show, Moreno was still on the pitch at full-time. Why would Klopp be so indulgent of such terrible defensive play?

It’s because when Moreno went in support of that attack, he was doing what Klopp wants him to do. He wants his team to play vertical, high-tempo attacking football and for that he needs full-backs who do more than sit and mind the house. Moreno was exposed when Lallana lost the ball, but that’s the risk you take as an attacking full-back. A team doesn’t score four at Arsenal without taking a few risks.

The ideal would be a player who had Moreno’s speed, stamina and attacking instincts without his propensity for errors. If Liverpool had found such a player they probably would have already signed him.