Another way in which Nick changes because of his relationship with the principal characters of The Great Gatsby is that he grows in wisdom and maturity.
His growth is seen primarily in his clearer evaluation of the motivations of such characters as the Buchanans and Jordan Baker. In particular, he gains the strength to see Jordan's selfishness for what it is, in spite of the strong intellectual and sexual attraction he feels for her. As he states in his last conversation with her, “I’m thirty,” I said. “I’m five years too old to lie to myself and call it honor” (Ch. 9).
However, Nick also gains the ability to step backwards from the particular social phenomena that he has been immersed in and take a broader view of what such creatures as Meyer Wolfsheim and the Buchanans say about America. In Gatsby's destruction, he sees the end of the American dream and the hope America once represented, dragged down by everything that had happened since:
He [Gatsby] had come a long way to this blue lawn, and his dream must have seemed so close that he could hardly fail to grasp it. He did not know that it was already behind him...
Gatsby believed in the green light, the orgastic future that year by year recedes before us. It eluded us then, but that’s no matter—to-morrow we will run faster, stretch out our arms farther. . . . And one fine morning——
So we beat on, boats against the current, borne back ceaselessly into the past. (Ch. 9)
In the first two pages of the novel, Nick explains the primary way he has changed since his move back from the East and his encounters with the Buchanans, Jordan Baker, and especially Jay Gatsby. Initially, Nick was raised by his father to "reserve all judgments" of people, since they "haven't had the advantages [he's] had."
After the events of the novel, Nick admits, he finds that his tolerance does have "a limit." He sees Tom and Daisy Buchanan as "careless people" who "smash up things and creatures and then [retreat back into their money," and Jordan Baker as a heartless liar. It is only Gatsby who is "exempt" from Nick's scornful reaction.