Final answer:
Gatsby initially tells Nick he inherited his wealth, which secured his mansion, but later amends his story to acquiring his wealth in three years, leading Nick to question Gatsby's truthfulness and the reality behind the American Dream.
Step-by-step explanation:
When talking about his mansion in The Great Gatsby, Gatsby initially implies that he acquired his wealth over a long period, suggesting it was inherited through family connections. This story begins to unravel when Nick presses him, and Gatsby amends his story, stating that his wealth was acquired in just three years. This discrepancy in Gatsby's story causes Nick to doubt the truth of Gatsby's past and raises the question of how Gatsby truly came into his fortune, signaling a pivotal moment in the reader's understanding of Gatsby's mysterious character. This incident underlines one of the main themes in F. Scott Fitzgerald's work - the elusive nature of the American Dream and the unreliable nature of Gatsby as a narrator.