One day, as Galba's grandfather was invoking sacrificial lightning, an eagle suddenly snatched the victim's intestines out of his hands and carried them off to an oak-tree laden with acorns. A bystander suggested that this sign portended great honour for the family. 'Yes, yes, perhaps so,' the old man agreed, smiling, 'on the day that a mule foals.' When Galba later launched his rebellion, what encouraged him most was the news that a mule had, in fact, foaled. Although everyone else considered this a disastrous omen, Galba remembered the sacrifice and his grandfather's saying, and interpreted it in precisely the opposite sense.
And thus a toss-off, dismissive joke becomes the inspiration for a man, signaling to him that he was destined to become Emperor of Rome.
-- Don't worry. It's good luck.
-- Yeah. In Haiti.