A diary is not a reliable source for understanding the true nature of a person, as people often avoid being completely honest with themselves in written form. The act of writing can sometimes be a way to conceal or distort reality rather than reveal it.
According to Lawrence Durrell in Balthazar, people tend to shy away from making honest confessions about love or other deep feelings, even to themselves. This reluctance suggests that self-reflection on personal emotions is often incomplete or guarded, making diaries an imperfect window into someone's true character.