Graphic: Five ways that Chelsea can beat Barcelona at the Bridge

Whatever has been going on under Petr Cech's black scrum cap these past few weeks, you wonder if it was a thought process anywhere near that of Jens Lehmann one Monday evening in late 2004 when he pitched up on the doorstep of Bob Wilson, the former Arsenal goalkeeping coach. Lehmann was, Wilson recalls, “psychologically disturbed”.

The German had, six months previously, completed an entire league season of unbeaten games for Arsenal and now he was wondering where it was all going wrong. He had just been dropped from the team. “He just wanted to ask, 'Did I deserve that?'” Wilson said. Wilson's answer was: “No, you did not.”

“He just needed support,” he added. “He needed putting back mentally.”

Here is another goalkeeper's dilemma, experienced by a Ray Clemence so young that he had not broken into the Liverpool first team: he found that he could not live with conceding a goal. “I used to take every one personally,” he said. “I was in danger of overreacting. Then Bill Shankly pulled me one day, he said, 'Look, the ball's got to have gone past ten of your team-mates before it's gone past you.'”

That was Shankly's way, Clemence recalls, of explaining that if you are a goalkeeper who blames yourself, “you will destroy your confidence”, which was maybe the same kind of precipice over which Lehmann was looking when Wilson pulled him back.

Which brings us to Cech, described as the best goalkeeper in the world, then a bloke experiencing a serious wobble and now a hero again. No one contributed more than Cech to the clean sheet that so frustrated Barcelona in the Champions League semi-final first leg at the Nou Camp on Tuesday night. “He saved the game for us,” were the words of Guus Hiddink, the Chelsea interim manager, who is not given to hyperbole.

The same Hiddink, a fortnight previously, described the same Cech as a man “not full of confidence”. There can be few more piercing assaults on a goalkeeper's confidence than the knowledge that your own manager is questioning it, which probably explains Cech's reaction: “Did the manager say crisis of confidence?” No, Petr, nearly but not quite.

Likewise, there can be few more exposed places in sport than standing on the goalline, knowing that an entire stadium knows you are dodgy. “If you dwell on it, you're dead,” Wilson said. “You may as well not be playing. If you go into your shell and stop making decisions, you have had it. You may as well give up.”

This is the analysis from Dr Steve Bull, the sport psychologist who will be working with the England cricket team during the summer's Ashes: “The goalkeeper, like the wicketkeeper, is an exposed position so when your form does start to go and you lose your confidence, it can be accentuated. They will start to feel isolated, lonely, they will feel the weight of the team and the outcome of the game on their shoulders.

“That's when the cycle of self-doubt, negativity, replaying your mistakes in your mind, can all set in. And once you are on the slippery slope, it can be hard to drag yourself back.”

There is, here, a vast gulf between loss of form and loss of confidence. One is temporary, the other can eat you alive. Lehmann was teetering on the latter but Wilson pulled him back.

Others have gone over the edge. On speaking to Alan Rough, the former Scotland goalkeeper, two came to mind immediately. First, Peter Bonetti. “I don't think he ever recovered from the 3-2 Germany-England game [in the 1970 World Cup quarter-finals],” Rough said. Second, Frank Haffey, after the England 9 Scotland 3 scoreline in 1961. “He certainly never recovered,” Rough said. “He emigrated to Australia.”

“There are certain games that have destroyed certain goalkeepers,” Rough added. And Cech? He seemed, on Tuesday, to inhabit the very opposite end of the spectrum.

In researching this article, we spoke to four goalkeepers: Wilson, Clemence, Rough and Steve Ogrizovic. This was before Tuesday's game, yet each said unerringly that Cech remained one of the world's best. Wilson suggested that he may improve if he shed the headgear, Rough said that his reading of crosses may always be his (comparative) weakness, yet they all shared two observations: 1) only because of his high standards has Cech been judged to have slipped a notch, and 2) we have all been through the same.

“Everyone has suffered the ignominy of an error of judgment and been made to look a fool,” Wilson said.

“And we've all had the thought, 'I hope he doesn't cross the ball now into my zone.'” Ogrizovic said.

“Most of us go down the tunnel thinking, 'Why am I subjecting myself to this?'” Wilson said. “It's a mixture of knowledge, fear, apprehension, knowing how unpredictable the role can be.”

The test of strength that Cech appears to have passed is that he has analysed only his mistakes and not his ability. He watched his quarter-final gaffes against Liverpool again and again and emerged stronger, not wondering if he will repeat them. That is the DNA of a world-class goalkeeper.

As Rough said: “It is always the goalkeeper's fault and you are brought up as a kid with that. The good 'keepers are the ones who can handle that. I always knew when it was my fault but for some reason it never fazed me.”

It would be inhuman not to feel the pain. Even a player as mentally stout as David Seaman was in tears twice - after Ronaldinho's goal in the 2002 World Cup quarter-finals and after Nayim's lob from halfway in the final of the Cup Winners' Cup in 1995.

But the key to Cech's form is that he has killed the pain. He has not turned up on Wilson's doorstep, there has been no psychological trauma. The dip was one of form, not of confidence, and he kept it that way. And Tuesday would suggest he is out the other side.