dictionaryofobscuresorrows:

n. a moment of awareness that someone you’ve known for years still has a private and mysterious inner life, and somewhere in the hallways of their personality is a door locked from the inside, a stairway leading to a wing of the house that you’ve never fully explored—an unfinished attic that will remain maddeningly unknowable to you, because ultimately neither of you has a map, or a master key, or any way of knowing exactly where you stand.