If you have played enough tournaments and league matches, nothing
@dingyibvs is saying is rocket science. Better players tend to be better by being able to do things at 80% effort that keep them consistent against worse players playing at 110% effort. When someone is stressed about losing to visibly better players, the problem is more about how they view their game than anything else, but it doesn't mean just changing their attitude will make them play better if playing better means better results. Almost all such players are clearly missing the in-between game with max consistency - they know how to play at 100 mph, and how to play at zero mph, but when you ask them to rally at 20 or 40 mph or 60 mph, they turn up their noses at such things in training and in matches because pros supposedly are hitting the ball with power all the time. A better player beats you with his consistency, rarely with his max power. Yes, you do need max power training, but that is not for every situation, just as max consistency training is not for every situation either.
Even look at Fan Zhendong vs Truls Moregardh in the Olympics final, in the beginning of the match, Fan tried to overwhelm Truls with power, probably still living in the afterglow of his semi-finals match vs Felix. But after it became clear that Truls was able to get such balls back and it was putting precisely the kind of pressure of Fan Zhendong that
@zeio described when going for high power shots, Fan reigned it in just a little bit without fully changing his game, so that he could remain consistent and play multiple shots and be more selective about when to go for the kill. A lot of your results are determined by the quality of your 70% game, people who are focused on the 100% game delusionally focus on how they play under ideal conditions and somehow forget all the misses when conditions are not ideal and then freeze up when the not ideal condition happens in a tournament match they cannot avoid or forget.
I will go so far as to say that anyone who doesn't build out a 40-70% effort spin based rally/placement game is both technically and psychologically deficient. It's the difference between being a player who can maintain his style against all kinds of opposition vs a player who plays well when things are at one speed, but who freezes up when the game is at a different tempo. The freezing up has side effects which show up when playing against extremely spinny or extremely slow players and other styles in general that mess you up. Sometimes, this includes lower rated players without the quality you are used to. Again, these things are all level relative.