The back half of the film is laced with misfortune (albeit with an underlying comic tone, brought on by Matt trying to keep things lighthearted).
One scene features Matt telling Owen he thinks he might be a “psychopath”—is this a cry for help or more play-acting? Shortly after, Owen has moved on and become just another face in the halls and another member of society the film specifically criticizes—his mind is elsewhere and he doesn’t see Matt as a friend in distress.
So, in a way, it’s Owen, Matt’s best and only friend, who actually drives Matt to do what he ends up doing in the end of the film.
As Owen fears for his own life when he sees what Matt has become, Matt doesn’t understand what’s changed and why he can’t see him for what he is, hence the line, “What are you doing? We know what’s really going on, but no one else does.
The main character of Matt is trying to become a movie star of his own creation.