I remember the year Real Madrid won their third in a row. They started awful, and they were doing terrible and had to make a lot of changes mid-season to be able to get back on top of things and win again. So I can easily say that three is a very difficult number, hell two is difficult, many clubs go decades trying and getting out of groups but failing to win it.
So it is smart to say that three in a row is a unique situation. But the main reason for that is that most of the players end up saying "W already won it, there is nothing else to prove anymore" and start playing worse. If PSG goes into that mode, they won't win. But if they play good again, then they will do fine. This is what it will decide it, if PSG plays with %100 then they will win, if not, they will lose.
Successful clubs in UEFA Champions League have something in common, they built up their squad with strong midfielders. With Barcelona, they had Xavi, Iniesta, Busquet; with Real Madrid they had Modric, Casemiro and Kroos; and with PSG they had Neves, Vitinha and Ruiz. From strong midfield, they have very good ability to control the match intensity and create very good second defensive layer to help defenders and goalkeepers reduce danger from opponent attacks.
With PSG, they have very young midfielders like Neves and Vittinha who will possibly be able improves themselves as well as have very long career ahead, and they are valuable assets of PSG in coming years. With these players, PSG will be able to go far in UEFA Champions League next seasons and they will likely win other Champions League titles in coming years.