Observation Haki lets you sense intent. The Voice of All Things lets you hear the soul of inanimate objects and animals (like Zunesha or the Sea Kings). Luffy has consistently shown the ability to sense emotions on a primal level—he knew Momonosuke was afraid, he sensed the sadness of Laboon, he heard the voice of the Sea Kings.
Luffy is the literal opposite. He is a hurricane of emotion. He fights with joy, rage, and impulsive chaos. In Gear 5, he laughs so hard he forgets to dodge. can luffy use observation haki
Observation Haki requires . It requires a serene, focused mind. Think of the users who excel at it: Rayleigh, Katakuri, Fujitora, even Enel. They are stoic, calculating, and emotionally flat during combat. Observation Haki lets you sense intent