Well, there's a lot to be discussed about what is the root cause of his lack of effort and his submissiveness when under pressure. That's an interesting discussion, because it is, undoubtedly, there. That defeated attitude before the game is over, I've seen it time and time again, vs Atletico two times, when ran a bit more than Pinto, vs Roma, even vs Liverpool (even though technically he played decently on Anfield), vs Bayern, vs PSG. What is it in Messi that makes him back way from the fight when the going gets tough?
I can imagine how Messi thinks/feels..
In fact, as exceptional he is as a player, he lacks a particular trait, which is: the Leadership.
Messi has grown as an introvert very shy boy, don't forget that. He is naturally hyper-sensitive. Nearly 15% of persons have this trait, which gives some strengths and some weaknesses too.
That said, Messi thrives when he is in a laser-focus mode, when he is fully immersed in the game, enjoying it to the heart. He needs to feel confidence and support to give his best. When he is under panick and heavy stress, he can lose the clarity of his mind which obviously can affect his performance (the alien mode disabled,lol).
Some players (especially the defenders and the midfield-horses) thrive in games under heavy stress and pressure. They give their very best when surrounded by a lot of frustration and unexcepted stuff. Others, like Messi, have a different mental setting.. There is nothing wrong about it, as it has its side of special strength too. But these special players/persons need to be trained, empowered, prepared to face any kind of situation, to consider it as a beneficial challenge for their growth, not something to fear that holds them back. I know the mental preparation in Barcelona hasn't been good during all the last seasons (compare it with J.Klopp's mental training!)
let’s hope. Would take a scrappy 1-0 with a penalty again though based on their terrible record in Bolivia.