What are some ways that The Reluctant Fundamentalist highlights the ways that a sense of self is determined by a person's social, political and cultural circumstances?

Two characters who demonstrate different senses of self that are strongly influenced by circumstance are Changez and Erica. While the notion of "determination" seems to eliminate free will, Mohsin Hamid does indicate that individuals make their own choices.
Changez decided, for example, to seek additional opportunities in the United States. Although he is from Pakistan, when he in his home country, he does not think as much about national identity as he does about how to maximize the opportunities presented by his class status. In his adopted country, however, his self-perception is influenced by others' views of him. Through the questions they ask, he learned more about their underlying assumptions.
His experiences in the US before and after the 9/11 attacks are night and day. The actions of individuals who others associated him with and the US political and social climate after that day helped change him. When he grew a beard—and his exterior appearance more closely aligned with those expectations—it also affected his interior identity.
Erica, a US-born woman, in contrast, does not think of herself primarily in terms of either race or class. She thinks of her identity as individual (although she is highly conscious of her gender), because she does not understand that white, class-based privilege allows her to ignore race. Her limited self-knowledge, heightened by her belief in a pure love (as experienced with her previous boyfriend), further precludes her lack of understanding concerning the profound effects that the 9/11 attacks have on Changez.