The word "内心" is formed through a direct and evocative spatial metaphor. It combines the character "内" (nèi), meaning "inside" or "interior", with the character "心" (xīn), which represents the "heart" not just as an organ but as the traditional seat of thought, emotion, and spirit. By placing "inside" before "heart", the compound visually and conceptually creates a layered image: the deepest, most interior chamber of the heart-mind. This formation does not describe a physical location but constructs a figurative space, pointing to the private, authentic realm of a person's true feelings, thoughts, and character that lies beneath the surface.