Truth.

'If no other knowledge deserves to be called useful but that which helps to enlarge our possessions or to raise our station in society, then mythology has no claim to the apellation. But if that which tends to make us happier and better can be called useful, then we claim that epithet for our subject. For mythology is the handmaid of literature; and literature is one of the best allies of virtue and promoters of happiness.'

-Thomas Bulfinch on fandom.