The true Fable, if it rise to its high requirements, ever aims at one great end and purpose representation of human motive, and the improvement of human conduct, and yet it so conceals its design under the disguise of fictitious characters, by clothing with speech the animals of the field, the birds of the air, the trees of the wood, or the beasts of the forest, that the reader shall receive advice without perceiving the presence of the adviser. 
There's a famous tale of the wolf who devoured the lamb. Despite the lamb's refutation of all the wolf's accusations against him. The moral of the story shows "The tyrant will always find pretext for his tyranny."
Reference:"A Dictionary of Ancient Greek Civilization".