According to Osho, a Buddha’s happiness is uncaused; it flows from choiceless awareness, egolessness, and freedom from desire. With nothing to gain or lose, he neither clings nor resists—he simply witnesses. Therefore outer events cannot disturb his inner sky; praise, blame, loss, or gain pass by, while his bliss remains self-sufficient and serene.
Buddha is happy because he wants nothing and just watches, so nothing upsets him.