In "The Sea of Monsters" by Rick Riordan, the narrator expresses a thought about someone who seems to have exhausted their supply of rocks. This implies a feeling of disappointment or disbelief regarding a character's actions or decisions. The mention of running out of rocks may symbolize a lack of resources or inspiration, suggesting that the character isn't living up to expectations.

By using this metaphor, Riordan enriches the narrative with an element of humor and relatability. The observation reveals the narrator’s perspective and adds depth to the ongoing situation, highlighting the challenges characters face in their journey. Overall, this quote encapsulates the themes of struggle and resourcefulness present in the story.