Happy people are more energetic and physically healthier than those who are not. And happiness adds about nine years to life expectancy. So even if you don’t think that happiness is such a big deal in itself, it seems to serve a useful instrumental function. Happy people are more likely than unhappy ones to change the world in positive ways.
“I readily agree that happiness isn’t everything. It isn’t even the most important thing. But all other things being equal, it’s better to be happy than not.”