This week, it's hit him between the eyes. The culture at Spurs. But it's been a slow burn. Postecoglou's outburst in the aftermath of Tuesday night was surely a long time coming.
When his appointment was announced, this column welcomed it - but with a warning. Not for the club. Nor the Tottenham support. Spurs were getting a top class manager. A winner. The warning, instead, was for the man himself. This club would let him down. These players would let him down. The culture that had eaten up Antonio Conte and Jose Mourinho would do the same with Big Ange.
But we were wrong. At least in terms of timing. Spurs have done well this season. The players have responded to Postecoglou's methods. There's been no whispering campaign emanating from inside the club's four walls (though let's see the reaction to Tuesday's post-match presser). And to be fair, losing Harry Kane on deadline day, the Australian would take a finish as we see now at the start of the season.
But Postecoglou isn't one to settle. He also isn't one to carry passengers. And the defeat to City encapsulated everything that will hold him and his ambitions back during this tenure.
"I just think the last 48 hours have revealed a fair bit to me," Postecoglou snapped. "That's alright. It just means I've got to go back to the drawing board with some things.
"Outside, inside, everywhere. It's been an interesting exercise.
"It's just my observations mate. I'm not going to tell you, because it's for me. I'm the one who's got to do it. You can make your own assessments of what's happened. I understand. I probably misread the situation as to what I think is important in your endeavour to become a winning team, but that's ok. That's why I'm here."
As we say, this game was an opportunity. For the players. The fans. A chance to beat a City team going for the title. The significance of that: a result against such a team and all that it entails. It's immeasurable - but it matters. In the growth of a team. Of it's young players. Such intangibles matter.
And they played well, did Spurs. But did they leave it all on the pitch? At the final whistle, Spurs pair James Maddison and Cristian Romero were seen laughing and joking with Pep Guardiola. Of course, your local observer would claim there's nowt wrong with that. But if roles were reversed. If Spurs had actually beaten City. Would Pep have even given either man a glance?
That's the difference. Especially at this level. It all matters. It all counts. The idea that Tottenham's players can be happy laughing and joking with the opposition manager after blowing their chance of taking fourth place into the final round is staggering. That it is simply accepted even more so.
And what of the fans? The small club mentality? Because that's what we saw in the lead-up and during the 2-0 reverse. A top four place was still up for grabs. The chance to beat the best team in the world was there for the taking. Yet the support were happy for the players to lay down and lose so to avoid Arsenal taking the title.
Again, Postecoglou post-match: "I can't dictate what people do. They're allowed to express themselves any way they want. But yeah, when we've got late winners in games it's because the crowd's helped us."
Crowd participation. Again, all this matters. If the fans aren't up for it. Indeed, if they'd rather the team were beaten. What's the point in Ange even turning up on the night?
This is the mentality that Postecoglou is now confronting. After all, this is the same club that sacked Jose Mourinho in the week of a League Cup final. The one manager with a history of pulling off the improbable through his tactical acumen. Yet he was sacked and replaced by Ryan Mason, a rookie with zero experience in the dugout. It's the same mentality that drove Conte into his rant and eventual departure last season. Just as it did with a fed-up Kane.
Postecoglou is a winner. From Australia, to Japan and Scotland. He's proven it. He isn't interested in courageous failures. Of being a nearly man. But this is what he's now working with at Tottenham. And the most sorry thing is that too few connected to Spurs actually understand Postecoglou's complaint.
Whether that stretches to the board room remains to be seen. But it was Daniel Levy, the chairman, who made that Mourinho call. And if the view is losing at home to City is no great setback, then you do wonder how long the Postecoglou era will last.