For this reason, nothing is impossible in football, sometimes we are sure the bet in the club is much stronger but in fact lost quite easily. This is sometimes in the prediction based on the statistics of the strength of the team. Regarding Real Sociedad and PSG PU. Statistically, actually PSG should have things that are much stronger both of them compete quite significantly and tightly. And it's true, whoever the winner is, they deserve for this, because sometimes the match at UCL is quite different in the euphoria. Either Mbappe will stay on PSG after the transfer market or not, this will definitely give a significant effect on PSG itself.
I think that the level of the competition can also set free a lot of mental elements that otherwise may not contribute as much to the game of a team. Real Sociedad may not be one of the strongest teams in La Liga at the moment, but they are certainly not one of the weakest teams either. If they have most of their important players available for the games against PSG, I think that the game could go either way (or the two games in aggregate for that matter). PSG should have some advantage over them, but even if you say that PSG is a 60% favorite, there is still a lot of room left for Real Sociedad to be successful against them in the Champions League.