The purpose of life is not to be happy.

"The purpose of life is not to be happy. It is to matter, to be of use, to have it make some difference that you have lived and lived well." - Leo Tolstoy
"Happiness is not the meaning of life; it is a result of living a meaningful life." - Jon Kabat-Zinn
"Life is neither happiness nor suffering. It is what you make of it." - Aldous Huxley
"Happiness and suffering are just byproducts of evolution, not its goals." - Daniel Dennett.
"Life is not a matter of holding good cards, but of playing a poor hand well." - Robert Louis Stevenson