In the book "Onyx" by Jennifer L. Armentrout, the protagonist experiences a moment of relief that underscores the tension and anxiety she has been feeling. The phrase "I let out a breath I didn't know I'd been holding" signifies the physical manifestation of stress finally being released. This moment represents the culmination of internal struggle and signifies a turning point in the narrative where the character can finally confront her emotions and reality.

This quote encapsulates the theme of navigating fears and uncertainties in the story. The protagonist's journey is marked by obstacles that create emotional weight, and the act of releasing her breath symbolizes not only personal growth but also the importance of vulnerability. As the story unfolds, such moments highlight the character's evolution and the deepening of relationships, emphasizing that acknowledging one's feelings is a crucial step towards personal empowerment and resilience.