Joy or positive emotions that we habitually experience with our inner being defines happiness. Such emotion, therefore, of delight and bliss starts from within us rather than by the stimulus that has caused the sense of satisfaction. You have a joyful experience seeing your grandchild, for example, an emotion that your wife does not share since she disliked her daughter-in-law very much. Caused outwardly at the surface by a particular stimulant, your happiness or unhappiness remains a subjective and personal option. Succinctly, it is you who choose to be happy!