Isolation leads to anger, hatred, and violence in The Lightning Thief. In the beginning, we learn that our narrator, Percy, is a lonely dude. He's often kicked out of schools because he's not "normal." Trouble seems to find him wherever he goes, and he has two learning disabilities (dyslexia and attention deficit disorder), making him truly feel like an outsider. Even when he has discovered that he has special powers and when he has found a place full of kids just like him, our narrator is still isolated and must stay in a cabin all by himself (thanks to his dad). When Percy feels alone in the world, he can be cold and angry. When he feels as though he has a place in the world, our he is full of courage and possibilities.
But Percy isn't the only one: Hades (the God of the Underworld) lives in loneliness underground, excluded from Mount Olympus by his brothers. The half-blood Luke resents his father, the god Apollo, for not being around or being interested in him. Isolation often results in violence, while connection and a sense of belonging often brings peace. That being said, Percy's isolation from society is also what makes him such a perceptive dude and an entertaining narrator – he notices and understands things about people in a unique way.