As far as I’m concerned, this is the greatest thing said about happiness by anyone ever:
This is the true joy in life, being used for a purpose recognized by yourself as a mighty one. Being a force of nature instead of a feverish, selfish little clod of ailments and grievances, complaining that the world will not devote itself to making you happy.
I am of the opinion that my life belongs to the whole community and as long as I live, it is my privilege to do for it what I can. I want to be thoroughly used up when I die, for the harder I work, the more I live.
I rejoice in life for its own sake. Life is no brief candle to me. It is a sort of splendid torch which I have got hold of for the moment and I want to make it burn as brightly as possible before handing it on to future generations.
George Bernard Shaw