In The Reluctant Fundamentalist, Changez (note the pun in his name: "changes") has a love/hate relationship with America. He thrives on the vitality of New York and his relationship with Erica (initially) can be seen as a parallel to his positive relationship with America. He achieves the "American Dream" so to speak, by going to an Ivy League school and landing a good job at Underwood Sampson. However, Changez is also disaffected by the American values he sees. For instance, Mike and Chuck seem to him too flippant. Erica's father acts condescendingly towards him. And he also notes that he was pleased with the bombing of the World Trade Center, seeing America "brought to its knees." As his relationship with Erica fades, so does his desire to compete at his job, and so does his desire to be the quintessential go-getter attitude of American capitalism.
Also, note that on page 98, Changez describes the "fundamentals" of his job with Underwood Sampson. Changez once excelled at following these fundamentals and as his identity and national affinity shifted from Pakistani-American to more completely Pakistani, he exchanges one set of fundamentals for another. The entire book is about Changez's change in national identity. The relationships he has with others express this change, so the tension is his identity shift but over the backdrop of West/East relations.