THE RAW MATERIAL OF A MYTH, like the raw material of a dream, may be something that actually happened once. But myths, like dreams, do not tell us much about that kind of actuality. The creation of Adam and Eve, the Tower of Babel, Oedipus—they do not tell us primarily about events. They tell us about ourselves.
In popular usage, a myth has come to mean a story that is not true. Historically speaking, that may well be so. Humanly speaking, a myth is a story that is always true.