Source identified1
“By being happy, we sow anonymous benefits upon the world”
The essay treats visible good spirits as a diffuse social contribution whose effects may reach other people without the cheerful person ever knowing where they landed.
Source note: “An Apology for Idlers,” 1877; evidence text in Project Gutenberg editions. The sentence belongs to Stevenson’s broader defense of leisure and sociability against relentless busyness.
Source identified2
“There is no duty we so much underrate as the duty of being happy.”
Stevenson argues that a person’s happiness can benefit others socially, so cheerfulness is not merely private pleasure in the essay’s deliberately provocative moral accounting.
Source note: “An Apology for Idlers,” first printed in the Cornhill Magazine in July 1877 and later collected in Virginibus Puerisque; represented through Project Gutenberg public-domain editions. The essay is polemical, not clinical advice about mood.