Final answer:
In the context provided, Nick's remembrance of his 30th birthday signifies a turning point and self-realization about aging, responsibility, and maturity, reflecting on what one has accomplished and the future.
Step-by-step explanation:
The query references a moment in literature where the character Nick recalls that it's his birthday, indicating a pivotal moment of self-reflection. Turning 30 often symbolizes a milestone in someone's life, usually representing the transition into full adulthood, with the ending of certain youthful freedoms and the onset of new responsibilities. This sentiment can carry an emotional weight, as there can be societal expectations tied to age. The quoted lines suggest a realization that youth is passing and one must show maturity and reveal their heart, aligning with themes of growth and identity.