Was thinking about Percy being kinda jealous of Nico because he's never not doubted who he is for a second and it made me think about the others regarding their connection or disconnection with identity and sense of self.
Annabeth and Piper feel connected to their sense of self, or at least their perceptions of who they are, even if that's not necessarily how they come across to others.
Clarisse struggles with it on occasion, especially as she works to be better and do better, but for the most part it's not the biggest concern for her.
Percy and Leo have way more issues with their identities. While Leo is a lot more confident in his answer to "who am I?", his response also contains an excess of negativity. Around people versus in isolation, it shifts constantly. He either views himself in terms of usefulness to others, as is what he can or cannot provide, or conceptually, like the blueprints of a machine. He struggles to see himself as a whole person on his own, rather than parts or components of a person.
As I've said so many times before, Percy builds his sense of self around his relationships with others. This makes it difficult when situations emerge where his gut instincts conflict with that identity or if the person behaves in opposition of that belief or how he expects. Sally's son is as calm and kind as she is, but he isn't. Best friends spend tons of time together, but Grover has his own life and responsibilities. Nico is powerful and doesn't need protection. There are so many clear instructions on how to be Annabeth's boyfriend, but he can't always follow them the way he's supposed to. When he fails to follow suit, he cracks. What is he without the people he loves?