Pep Guardiola is at a crossroads and the decisions he makes in the next few weeks and months will define his time as Manchester City boss.
I'll say it until I'm blue in the face. He has made a huge mistake in ploughing ahead with the wild notion that goalkeepers should be able to play on the deck and that full-backs must play as midfielders.
Strip that down to bare bones and the stupidity of it is laid bare. I hardly even need to explain it because the evidence was there for everyone to see in that 4-2 defeat by Leicester.
Instead of encouraging his goalkeeper to clear his lines as his first thought, he tells Claudio Bravo that he must be willing to play the ball out.
Instead of telling his full-backs to defend and hold their positions, he has them running into central midfield.
Instead of telling John Stones to put his foot through the ball if he's in bother, Guardiola tells him to play his way out of trouble around his own penalty area.
He does all of this in the Premier League, a high-tempo, high-pressure environment very different from the Bundesliga or La Liga, neither of which contains teams all the way down to the relegation zone capable of matching your players for effort, fitness and motivation.
I know he tried these things in Munich for a while but abandoned them and he may ever have been experimenting with it at Barcelona though to be honest, I don't think we would have noticed if he was.
The players were so good there that it wouldn't have mattered much what way he lined them up because they would have found a way to win.
But what we do know from his time at Barcelona is that he had little time for defending and truly believed that his team would score more than the opposition every time
He was right about that but only because of the players. It would be hard to fail when you can pick from Messi, Iniesta, Xavi and a long list of other top notch footballers. It is funny because we are debating in a very refined atmosphere here. This is not a discussion about whether Guardiola is a good manager or not. His record speaks for itself.
But he is facing a challenge at the Etihad which he has never had to cope with before.
If we look at what he achieved at Bayern Munich, we see that Jupp Henkel who came before him finished with a treble, including the European Cup.
Guardiola did win three league titles in a row in Germany but couldn't win the Champions League. He was expected to improve on his predecessor but he did not.
The fact that Carlo Ancelotti is now struggling with Bayern tells its own tale.
Now Guardiola is standing in a harsh spotlight in Manchester, with critics getting louder by the day and his team showing the kind of inconsistency which is inevitable if a manager insists that his players continue with a mad experiment which very clearly does not work.
He is not alone in dream ing up a big new idea. On a smaller scale, I remember Don Revie switched Norman Hunter into midfield and Paul Madeley to defence because he thought he would get the benefit of extra bite in midfield.
It didn't work and after two or three games, he quietly switched Norman back and it was never mentioned again.
Alex Ferguson had some notion that he had to set-up his players differently in the Champions League during the 90s and it took him a few seasons to work his way through to the other side of that.
The important thing here is that both managers realised that they had made a mistake and corrected the error.
That is exactly what Guardiola must do now. He must sit down, look in the mirror and tell himself that he must stop tampering with football fundamentals because of his conviction that he has found a new way to play that is better than anything that went before.
Very few managers are ever afforded the licence to play around like this. Guardiola's achievements to date and the cult which has built up around him have given him that latitude.
But the Premier League is a mincer and will spit him out just as easily as it humbled Louis van Gaal.
Antonio Conte is showing what can be done when you establish, good, basic defending as your platform. He is the standard at the moment and Guardiola is falling well short of matching it.