He just started to believe the media hype that he is one of the best managers in the world. He wanted to prove this, and PSG was literally one of his only chances for that. Cause he needed guaranteed titles.
Clubs that can promise it -
- PSG
- Bayern
- Ajax
- Juventus
He needed one of them to prove that he can do it. In Dormund he would have ended up like he did with us most likely. Dormund is not dominating Bundesliga, in fact it is super unlikely to win much there. Would have been "almost-man" there as well. So, he essentially believed he is better then he was and I think he will be in for reality check. Maybe better option would have been to take over some reasonably managed club that would give some time to managers - but he did not take this path.