This is true because each person or god has their own perception of what is pious and impious. In each city there is a different god, since all the gods do not agree and do not have the same perception of what is pious and impious, there is no exact definition of piety, "different gods consider different things right, beautiful , ugly" , good and bad, since they would not disagree with each other unless they differed on these matters” (Plato's 5 Dialogues, Euthyphro pag.9, 7e). Plato wrote the book Euthyphro to raise public awareness of the existence of a new way of thinking. Most people thought that all gods thought the same. However we can clearly see that not all gods agree on everything and that there is no one way to do it