The Lightning Thief
How we cite our quotes:
The attack had scared everybody. It sent two messages: one, that I was the son of the Sea God; and two, monsters would stop at nothing to kill me. They could even invade a camp that had always been considered safe. (9.5)
Percy feels like a menace no matter where he goes. Just when he found a safe place, a place to really call home with kids like him all around, he becomes a threat to that very place. He is a destructive force. He doesn't really know yet that the reason he is a destructive force is that he is really powerful.
Even here in the Underworld, everybody—even monsters—needed a little attention once in awhile. (18.199)
Poor old Cerberus really wants someone to play with him. The Lightning Thief teaches us that being lonely and isolated sucks for mortals, monsters, and gods alike. There is a universal desire among all beings to connect with or interact with others.
But I thought of how few people there were in Elysium, how tiny it was compared to the Fields of Asphodel or even the Fields of Punishment. So few people did good in their lives. It was depressing. (19.14)
Percy seems to comment here that even if you do really good things in your life and make it to Elysium (like heaven), things will be a little lonely there. You won't have as much company as if you hung out on the Fields of Asphodel. Maybe having company doesn't matter to a dead spirit, but it sure matters to a living one.