The word 不在乎 is formed through a conceptual fusion where the negating prefix 不 (not) combines with the classical verb-particle construction 在乎 (to be at/in, to care about), which itself visually and notionally anchors concern as something "located within" a sphere of regard. By adding 不, this locative metaphor for caring is inverted, creating a fixed phrase that conveys the idea of something being intentionally left outside one's sphere of attention or concern, thus meaning "to not care about" or "to disregard".