There is no duty we so much underrate as the duty of being happy. By being happy we sow anonymous benefits upon the world. – Robert Louis Stevenson
. . . because it has two important benefits:
1) you get to be happy
2) you serve as a living, breathing model of what to do.
The Worlds are better when you’re happy (your world. i.e. your experience; and the larger World benefits by having another happy person in it.)