So he invented just the sort of Jay Gatsby that a seventeen-year-old boy would be likely to invent, and to this conception he was faithful to the end
As human beings, both our goals in life and the situations of the world around us generally fluctuate. However, some people have aspirations so strong that they hold onto them for their entire lives (“faithful to the end”). Early in his lifetime Gatz created the concept of what he wanted to be when he grew up, and refused to let go of this dream as long as he lived. Although he appears to be faithful to the person he truly is at heart, James successfully manipulates the exterior of his person, creating for himself everything from a new name to massive amounts of wealth. However, Fitzgerald hints that James' true self is still steadfastly intact, and that he is unable to alter his genuine personality/disposition
The persona of Jay Gatsby is, from Nick’s perspective, the realization of an immature fantasy. Gatsby is “just the sort” of character “that a seventeen-year old boy would be likely to invent”; this suggests that there is something naïve or childish about the character that he creates for himself.
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