In "Paul's Case" why does it always repeat things about Paul's smile? in other words, what is the significance of the smile?

When Paul goes in to face the school faculty, he is smiling in order to present himself as "suave" and confident. He continues smiling. When other, older boys had to face the faculty in similar ordeals, some would break down crying or at least give the appearance of expressing remorse or humility. But Paul smiles to convey that he is above it all. He wants them to know that their disapproval means nothing to him....

When Paul goes in to face the school faculty, he is smiling in order to present himself as "suave" and confident. He continues smiling. When other, older boys had to face the faculty in similar ordeals, some would break down crying or at least give the appearance of expressing remorse or humility. But Paul smiles to convey that he is above it all. He wants them to know that their disapproval means nothing to him. He wants them, and everyone, to know that he doesn't belong in this school; his real home is somewhere else. He smiles out of defiance and they recognize this, interpreting it as arrogance or some mental problem: 

Paul was always smiling, always glancing about him, seeming to feel that people might be watching him and trying to detect something. This conscious expression, since it was as far as possible from boyish mirthfulness, was usually attributed to insolence or "smartness." 

When Paul is in the theater, his smile is genuine. There, he is genuinely happy. This is ironic because in other aspects of his life, his smile is fake. It is a means to convey his confidence and defiance. It is an act. In these instances, it is a "nervous" smile or a "frightened" smile. But in the theater, where people are always "acting," his smile and his behavior are real and genuine. It is only in the theater or social situations connected with the arts, that Paul feels comfortable and happy enough to smile genuinely. Paul's "case" (in medical or psychological connotations) is that the only feels happy and "real" when he is in situations associated with the theater and the arts. In other words, he only feels natural in situations associated with acting and the realms of creativity and fiction.