Rick Riordan said this quote

Hades allowed himself the faintest smile, but there was nothing cruel in his eyes. ‘I can entertain the possibility that you acted for multiple reasons. My point is this: you and I rose to the aid of Olympus because you convinced me to let go of my anger. I would encourage you to do likewise. My children are so rarely happy. I … I would like to see you be an exception.’ Nico stared at his father. He didn’t know what to do with that statement. He could accept many unreal things – hordes of ghosts, magical labyrinths, travel through shadows, chapels made of bones. But tender words from the Lord of the Underworld? No. That made no sense.