In Greek mythology, Apollo descended from the heavens onto earth in order to seduce the beautiful Cassandra. As a gift, he gave her the gift of prophecy. But when she rejected him, he told her she could still keep her gift with the consequence that no one would believe her.
Unfortunately, Cassandra was the daughter of Priam, King of Troy. After ten years of fighting in the Trojan War, the Greeks apparently got up one day and left, leaving behind a massive wooden horse at the gates of the heavily fortified and impenetrable Troy.
Cassandra cried, pleaded and begged her father and everyone around her not to let the horse into the city, or else Troy will fall that night. But everyone took her for a hysterical exaggerator and they welcomed the Trojan Horse into the city.
Troy burned that night.
And we never learned our lesson.