Objectively you can't prove that it [is not], but you can choose to believe that it [is not].

Soc. Alas! my companion, and will you leave me in despair? I was hoping that you would instruct me in the nature of piety and impiety; and then I might have cleared myself of Meletus and his indictment. I would have told him that I had been enlightened by Euthyphro, and had given up rash innovations and speculations, in which I indulged only through ignorance, and that now I am about to lead a better life.