those who, like Tiresias, have seen and come into touch with the mystery of the two serpents and, in some sense at least, have been themselves both male and female, know the reality from both sides
Campbell argues that Tiresias’s bisexual transformation confers unique metaphysical knowledge, explaining why he alone among the dead retains full understanding in Hades.
, Occidental Mythology: The Masks of God, Volume III, 1964thesis