What literary devices or style did Nick Hornby use in High Fidelity to exaggerate selfishness in Rob's behavior?

I think that one of the strongest literary devices that
Hornby uses is the fluid nature of Rob's character.  Rob is not shown to be static.  In
fact, he is quite the opposite.  Hornby wants to bring out the emotional frailty that
resides underneath an exterior of musical elitism and the idea that great art and great
artists must suffer.  He shows Rob to be a character who recognizes his faults in the
darkest recesses of his being, yet one who would never admit them for fear of being
hurt.  It is this idea of needing to take risks and needing to embrace the fear and
insecurity that is the basis of not only all great art but living and being in the world
that makes Rob such an interesting character. However, the process to reach this point
is a volatile one and an element that brings out Rob's selfishness in his attempt to
make peace with his own sense of identity.  Hornby is able to bring this out through his
fluid characterization of Rob.  At one moment, Rob's sensitive nature is what makes his
admirable to the reader.  Yet, at the very next moment, when confused and frustrated,
Rob's venom is what repulses.  This emotional selfishness and indulgences is what Hornby
brings out in Rob.  In showing Rob in this manner, with both elements valid expressions
of his state of being in the world, Rob is shown to be someone struggling to find
himself.  Like all pursuits in this manner, it is a self indulgent and narcissistic one,
but one that Hornby argues is an essential one to find happiness and some sense of peace
in a world that lacks both elements.