How has culture shaped the lives and attitudes of the main character in The Great Gatsby?

If Nick is considered the main character, then the culture
in the quiet interior of the country has made him a practical, rational man who yearns
for adventure and success but who can still see folly and misguided--even
destructive--choices. This is amply underscored by the fact that at the end of his
experiences with Gatsby, after attending Gatsby's funeral, Nick returns to his homeland
in the Middle West, thus leaving the pain of Gatsby’s failed Eastern life behind. As he
says:

On the
last night, [I] looked at that huge incoherent failure of a house once
more.

If Gatsby is considered
the main character, as the narrative is about Gatsby and his self-deceiving
belief

in the
green light, ... that year by year recedes before
us,

then the cultures
represented by multiple backgrounds and mentors has made him a man who lives by
deceptiveness, which he wittingly and unwittingly applies to his dealings with others as
well as to his own personal beliefs. Nick summarizes Gatsby's culturally influenced life
of deception and self-deception by saying:

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his dream must have seemed so close that he could
... grasp it. He did not know that [the future] was already behind him ... borne back
ceaselessly into the past.