Disillusionment is a central theme in The Great Gatsby, reflecting the shattered illusions of the American Dream and the moral decay of the 1920s. Through the characters and their experiences, Fitzgerald critiques the idea that wealth and status can bring true happiness and fulfillment. The novel reveals the emptiness behind the glamorous facade of the Jazz Age, exposing the disillusionment that follows the pursuit of superficial dreams.

One aspect of disillusionment in the novel is the revelation of Gatsby's true identity. Initially, Jay Gatsby appears as a wealthy, enigmatic figure, but as the story unfolds, it is revealed that he was once James Gatz, a man of humble origins. This transformation from Gatz to Gatsby symbolizes the illusion of self-made success. The grandeur of Gatsby's persona is diminished by the truth of his past, highlighting the disappointment in the American Dream's promise of upward mobility.

The disillusionment extends to Gatsby's lavish parties, which are initially seen as symbols of opulence and excitement. However, Nick Carraway, the narrator, describes a "pervading harshness" at these gatherings, suggesting a sense of emptiness beneath the surface. The parties, much like Gatsby's life, are built on illusions and fail to bring genuine joy or connection. This reflects the broader theme of disillusionment with the materialistic culture of the time.

Gatsby's unwavering hope and idealism also contribute to the theme of disillusionment. Despite his wealth and efforts, he cannot recreate the past or win back Daisy Buchanan's love. His belief in the "green light, the orgastic future" is ultimately unattainable, symbolizing the elusive nature of the American Dream. Nick observes that Gatsby's dreams are constantly "borne back ceaselessly into the past," illustrating the futility of chasing an idealized future.

Nick Carraway's own disillusionment is evident in his reflections on the other characters. He is disenchanted with the superficiality and moral decay of East Coast society, particularly the Buchanans, who embody the corruption and carelessness of the wealthy elite. In contrast, Nick admires Gatsby's "extraordinary gift for hope," yet he recognizes the tragic consequences of Gatsby's relentless pursuit of his dreams. This disillusionment with humanity and the American Dream underscores the novel's critique of the era's values and beliefs.