There is no duty we so much underrate as the duty of being happy. By being happy, we sow anonymous benefits upon the world, which remain unknown even to ourselves, or when they are disclosed, surprise nobody so much as the benefactor.

Robert Louis Stevenson (1850-1894) Scottish essayist, novelist, poet

Essay (1877-07), “An Apology for Idlers,” Cornhill Magazine, Vol. 36
    (Source)

Collected in Virginibus Puerisque and Other Papers, ch. 3 (1881)