Kafuku expresses deep pain over not fully understanding someone important to him, which leaves a lasting sense of loss. He reflects on the idea that some aspects of her being remain inaccessible to him, almost like a mystery that is now buried forever. This lack of comprehension contributes significantly to his sorrow, highlighting the emotional weight of missed connections in relationships.

The metaphor of a locked safe at the ocean's bottom symbolizes the valuable but unreachable parts of the person's identity that Kafuku could never unlock. This imagery powerfully conveys the regret that accompanies grief, emphasizing how unresolved feelings can linger long after a loved one is gone. Kafuku’s anguish over this unknowing illustrates the profound impact of unexpressed understanding in intimate relationships.