When a player could not score a penalty is actually his fault because he was the one that was given the opportunity to play, so there is no two ways about it but however the only thing is that nobody is above making a mistake and fate shouldn't even be the reason because confidence is much higher than fate because without confidence no matter how many times you play you would always loss a lot but is not that having a confidence guarantee your scoring because he was very confidence but is just unfortunate for him that the goalkeeper had already have that direction in mind, so actually confidence only gives you a higher chance of scoring a penalty.
Self-confidence is always an important thing that anyone must have if they want to maximize their potential or abilities. This includes professional football players. He must always appear confident and if someone loses self-confidence then he will not even be able to maximize his own abilities.
And I think that's what happened to Mbappe. because in fact he is a very great and talented player but he always seems to lose confidence when he is faced with big responsibilities such as executing penalty kicks. And this made him unable to maximize his abilities at all. But I'm sure that when he regains his confidence he will return to his best performance again.