Nico experienced profound loneliness after the loss of his sister Bianca. This grief led him to alienate other demigods who attempted to connect with him, reinforcing his isolation. His past encounters at Camp Half-Blood, along with his harrowing journey through the Labyrinth and Tartarus, have left him deeply traumatized. As a result, he struggles with trust and forms of attachment.

The weight of his experiences has made Nico wary, forcing him to build walls around himself. He grapples with his emotions, haunted by the loss and the scars of his adventures. The impact of his choices and the fear of losing more people he cares about significantly contribute to his sense of solitude.