The only thing done just for itself, instead of as a means to get something else, is the act of trying to be happy. Why do you want money? Why do you want a nicer car? Why do you want recognition from your friends and family? Why do you want love? You want these things because you think they will make you happy. And some will. And some will for a short time. And some will for a long time.
Happiness is the only thing done for itself and not as a means to any other end.
The inspiration from this originally comes from Aristotle:
Happiness is… “that which is always desirable in itself and never for the sake of something else”