why does amir change everything around him to fit his own personality rather than shape himself to society?

Early in the book, Amir is a young child and does not have the maturity to understand his motivations. He craves the attention and acceptance of Baba and tries to shape his life so he can get it. He tries, often at the expense of Hassan his friend and half brother. It is not until much later in the book when Amir, as an adult, really understands the motivation and implications of his actions.