Many people think that the essence of human life, its meaning and purpose, should be rooted in no other thing but to be as happy as possible.
There are others who believe, on the contrary, that a life is only worth living if it is useful to others and if it brings something to the world.
Personally, I believe that altruism is a good criterion for a successful life, and the only worthwhile life: a life is only successful if the world is, after the life has ended, slightly better because that life existed.