This is perhaps a not unimportant counsel to give to writers: write nothing that does not give you great pleasure; emotion passes easily from writer to reader.

[Ce ne serait peut-être pas un conseil peu important à donner aux écrivains, que celui-ci: n’écrivez jamais rien qui ne vous fasse un grand plaisir; l’émotion se propage aisément de l’écrivain au lecteur.]

Joseph Joubert (1754-1824) French moralist, philosopher, essayist, poet

Pensées [Thoughts], ch. 23 “Des Qualités de l’Écrivain [On the Qualities of Writers],” ¶ 58 (1850 ed.) [tr. Lyttelton (1899), ch. 22, ¶ 25]
    (Source)

(Source (French)). Alternate translations:

This were perhaps not an unimportant advice to give to writers: never write any thing that does not give you great enjoyment; emotion is easily propagated from the writer to the reader.
[tr. Calvert (1866), ch. 15]

And perhaps there is no advice to give a writer more important than this: -- Never write anything that does not give you great pleasure.
[tr. Auster (1983)], 1823 entry]