Colossal vitality of his illusion.
The idea of Daisy that Gatsby has been cultivating all these years is an illusion of perfection, of immense “vitality” and life. Daisy may not be living up to the expectations that Gatsby has set for her, expectations that have been built and imagined upon from their love affair from five years ago. It’s possible that Daisy has grown out of the woman that she was then, and isn’t the same girl that Gatsby is so madly in love with.
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