His problem is he puts too much pressure on himself to be that guy that makes shots and he is hurrying and forcing too much. He needs to concentrate on defense, let the game slow down and have the game come to him.
I think, unfortunately, for some, the expectations are just a continuation of what he did in 5 minutes to a Cleveland team that had mostly G Leaguers playing against him. The reality is NBA players and defenses are much faster, better and more advanced than those that he saw in preseason, and Carsen needs to adjust.
Once he does, he will be fine but expecting Carsen to go 4 for 5 or 6 from three every game just isn't realistic. I'll be happy if he can just hit his threes at a 35% rate or higher(even if he is just taking 3-4 total field goals a game)and plays great defense.