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.
To be honest, I don't see any chance for Real Sociedad to beat PSG. They simply lack the strength to take on the superstars of PSG.
In my opinion the following teams will reach the next round:
Real Madrid
Manchester City
PSG
Bayern
Dortmund
Inter
Arsenal
Barcelona
There are always surprises, this time Barca could possibly be one.
If it was that easy, why did they even play the final in the Champions League last season when Manchester City took on Inter Milan? Because on paper the game was long over before it started, but then we saw a final played by two evenly strong teams. It's not about what would normally happen, it is about circumstances that can emerge from within the game. Little details can change everything. Thought that West Ham would beat Arsenal? Or that Manchester United turns 0-2 into 3-2? Or that Nottingham beats Newcastle? The same happens in the Champions League. Shakhtar has beaten Barcelona for example. PSG has an advantage, but wait for the game.