The morale of the club boost since they won the UEFA champions league this season. It's been really a crucial run for the club since Luis Enrique took over as running manager. He put in the work and mind to the game and look at the height they've reach this season. Paris Saint-Germain will continue to triumphed because they're no longer playing just to satisfy themselves, rather they're playing good football with equal accolades to everyone.
PSG three season back was something else, they failed in all scenario to adopt a pattern that works for them when it comes to competing in elite tournaments. Les Parisiens was only known for lifting domestic titles but now, we can say the same because they won the UCL and that makes them reigning UCL champions. They worked hard for it and they deserve it.
I think that having a very high morale cannot also increase the confidence and security to face the matches.
Unfortunately, it is a known fact that when you are doubtful or when you are not sure of yourself, you cannot give 100% of what you can give.
So morale and self-confidence can only reinforce what already exists.