A shepherd boy, who tended his flock not far from a village, used to amuse himself by crying out, "Wolf! Wolf!" Twice or thrice his trick succeeded. The whole village came running to his assistance, only to be laughed at for their pains.
One day, the wolf came indeed. The boy cried out in earnest. But his neighbors, supposing him to be at his old sport, paid no heed to his cries. The wolf devoured the sheep.
So the boy learned, when it was too late, that liars are not believed even when they tell the truth.