It is true that Real Sociedad performed well in UCL. They could finish the group stage as the leader of the group D. It is quite interesting because they are in a better position than Inter Milan. We know that the point is the same, but Real Sociedad has lower conceded goals. It means the defense of Real Sociedad is quite solid, it won't be easy to defeat by other teams.
They will play against PSG in the next match, I'm also sure that Real Sociedad must have the chance to win. PSG seems not playing very impressively, they were almost eliminated in the group stage. PSG was also conceded many goals during the matches in the group stage. It makes me a bit doubtful with the performance of PSG. Their defense looks not strong enough to compete with a strong team. Although Real Sociedad attackers aren't top players, they could destroy PSG defense as it seems rather weak. Meanwhile PSG attackers will struggle a lot because Real Sociedad has a solid defense.
I have no doubts that the Paris Saint-Germain squad can beat Real Sociedad in the first leg, especially since the first leg will be played at PSG's home ground, of course this is a strength in itself playing in front of its supporters. But I doubt paris saint-germain will hurt themselves again. They did this against Newcastle, and Dortmund. The Paris Saint-Germain squad can sometimes be its worst enemy.

But Real Sociedad is also very strong at home, so I think Paris Saint-Germain and Sociedad will perform well in both legs. Even though Real Sociedad is one of the clubs that looks like a weak team, Paris Saint-Germain should not underestimate Real Sociedad. My prediction is that this match will take place in the round of 16. First leg: Paris Saint-Germain won 3-0 Second leg: Real Sociedad won 1-0.
With the kind of impressions that Real Sociedad came with in the champions league this season, I don't think Paris Saint German will have an easy way with them even with the fact that PSG is playing at their home ground but i see Real Sociedad making things look difficult for PSG, and you know PSG have a very porous defense whereas Real Sociedad's defense is very organized that's why if you check most of their matches, they don't actually concede much goals so PSG will find it difficult to maneuver their defense. And moreover, we all saw that PSG never really put more effort in the group stage matches as it was just out of luck that they were able to reach the knockout stages and even if PSG wins Real sociedad I believe that Real Sociedad will also retaliate when PSG visits them in their home ground.