For John Stones, it will haunt him for the next six weeks or so.
Right up until England’s manager selects his 23-man squad for the European Championships.
This was a reminder of what you get from Stones; the flaw in his make-up that can prove catastrophic.
His face said it all. It had all gone so well.
He spoke last week with pride at having forced his way back into the England picture after an absence of more than a year. He also praised the ruthless side to Southgate for having the guts to make the tough calls.
Now Stones needs to hope for leniency from a man, who most recently axed Trent Alexander-Arnold from his set-up.
Controlling a simple pass from Nick Pope, his touch was heavy, his mind was sloppy.
Jakub Moder harried him out of possession.
Arkadiusz Augustyniak cut the ball inside and Moder was there to fire past Pope to equalise after Harry Kane’s first half penalty gave England the lead.
These are the moments that kill ambitions of winning major tournaments.
Yes Stones rose high in the last five minutes to head into the path of Maguire, who finished like a striker to keep the Three Lions in control at the top of Group I - but against better opposition there may be no second chance.
All that hard work thrown away because of a slip of concentration – an errant touch.
We’ve been here before with Stones, whose two blunders cost England in their Nations League semi-final defeat to Holland in 2019.
This season he has looked rehabilitated alongside Ruben Dias at City. The question is – just how much heavy lifting has his defensive partner had to do in that relationship?
Guardiola encourages Stones and the rest of his players to build out from the back – as does Southgate.
Guardiola believes it will create more goals than it will cost his team over the course of a season.
That may be the case – but tournament football is an entirely different story.
One moment like this and it could all be over. No second chance. No three points on offer a week later once you reach the knockout stages.
And that’s why Guardiola should be concerned, too.
The Premier League is wrapped up. The only games with jeopardy as far as City are concerned are in knockout competition.
The Carabao Cup final against Tottenham; an FA Cup semi-final against Chelsea.
And the big one – the Champions League, which has been Guardiola’s downfall at City.
Stones cannot afford to give Erling Haaland an opportunity like that when they face Borussia Dortmund in the quarter-finals – or any opponent from hereon in.
While that is not Southgate’s concern, Stones’ reaction when back with his club will be instructive for the rest of the season.
That horror moment has the potential to plague him.
That is the culture Southgate has created with England – the fear of knowing no place is guaranteed. No place is safe.
But even Stones does resume his imperious form when back in City blue, this was a warning that Southgate simply cannot ignore.
Phillips emerges as key figure
Much has been made of Mount establishing himself as a definite starter in England’s midfield - but Kalvin Phillips is doing likewise on the quiet.
He has started all three of these World Cup qualifiers and it is easy to see Southgate’s preferred midfield taking shape now.
Phillips has made incredible strides over the past 12 months – from the Championship with Leeds to a potential starter at a major tournament.
So much credit needs to Marcelo Bielsa, who has nurtured his talent and provided England with a cultured midfielder, who looks totally at ease on this stage.
Kane on the spot
Kane is now England’s all-time leading scorer from the penalty after converting a 10th for his country.
That takes him one clear of Frank Lampard.
Heading into a major tournament – and given England’s history in shoot-outs – it is comforting to know we have a master from 12 yards