água mole em pedra dura, tanto bate até que fura

The proverb’s image has classical Latin parallels. A commonly circulated formula is gutta cavat lapidem, non vi sed saepe cadendo, "the drop hollows the stone not by force but by falling often". Ovid’s actual verse in Epistulae ex Ponto, IV.10.5, reads gutta cavat lapidem, consumitur anulus usu, "the drop hollows the stone; the ring is worn away by use". The expanded formula is not the wording of that passage. A related idea appears in Lucretius, De rerum natura, I.313: stilicidi casus lapidem cavat.