We should laugh before being happy, for fear of dying without having laughed.

[Il faut rire avant que d’être heureux, de peur de mourir sans avoir ri.]

Jean de La Bruyère (1645-1696) French essayist, moralist

The Characters [Les Caractères], ch. 4 “Of the Heart [Du Coeur],” § 63 (4.63) (1688) [tr. Stewart (1970)]
    (Source)

(Source (French)). Alternate translations:

We must laugh before we are happy, or else we may die before we have cause to laugh.
[Bullord ed. (1696)]

We must laugh before we are happy, for fear we die before we laugh at all.
[Curll ed. (1713)]

We must laugh before we are happy, or else we may die before we ever laugh at all.
[Browne ed. (1752)]

We must laugh before we are happy, or else we may die before ever having laughed at all.
[tr. Van Laun (1885)]

We must laugh before we are happy, for fear of dying before we have laughed.
[tr. Lee (1903), "Brief Reflections on Men and Things"]