In the movie "Palm Springs," the main characters' personalities evolve as they are forced to relive the same day in a time loop. At first, Nyles seems carefree and nihilistic, while Sarah is more cynical and self-destructive. However, as they spend more time together and face the consequences of their actions, they start to grow and change. Nyles becomes more introspective and begins to question the meaning of his life, while Sarah learns to let go of her past regrets and embrace the present moment. Overall, the time loops allow the characters to confront their flaws and insecurities, leading to personal growth and deeper connections with each other.