If Jupiter hurled his thunderbolt as often as men sinned,
he would soon be out of thunderbolts.
The source for the proverb is Forty Thousand Quotations: Prose and Poetical by Charles Noel Douglas (Bartleby.com). Ovid's words are: Si, quotiens peccant homines, sua fulmina mittat / Iuppiter, exiguo tempore inermis erit. The poster is made with AutoMotivator. The image is a statue of Jupiter at Schwarzenacker found at Wikipedia.