Never try to teach a pig to sing; it wastes your time and it annoys the pig.
—Robert A. Heinlein
In Persia many centuries ago, the Sufi mullah or holy man Nasruddin was arrested after preaching in the great square in front of the Shah's palace. The local clerics had objected to Mullah Nasruddin's unorthodox teachings, and had demanded his arrest and execution as a heretic. Dragged by palace guards to the Shah's throne room, he was sentenced immediately to death.
As he was being taken away, however, Nasruddin cried out to the Shah: "O great Shah, if you spare me, I promise that within a year I will teach your favourite horse to sing!"
The Shah knew that Sufis often told the most outrageous fables, which sounded blasphemous to many Muslims but which were nevertheless intended as lessons to those who would learn. Thus he had been tempted to be merciful, anyway, despite the demands of his own religious advisors. Now, admiring the audacity of the old man, and being a gambler at heart, he accepted his proposal.
The next morning, Nasruddin was in the royal stable, singing hymns to the Shah's horse, a magnificent white stallion. The animal, however, was more interested in his oats and hay, and ignored him. The grooms and stablehands all shook their heads and laughed at him. "You old fool", said one. "What have you accomplished by promising to teach the Shah's horse to sing? You are bound to fail, and when you do, the Shah will not only have you killed - you'll be tortured as well, for mocking him!"
Nasruddin turned to the groom and replied: "On the contrary, I have indeed accomplished much. Remember, I have been granted another year of life, which is precious in itself. Furthermore, in that time, many things can happen. I might escape. Or I might die anyway. Or the Shah might die, and his successor will likely release all prisoners to celebrate his accession to the throne".
"Or...". Suddenly, Nasruddin smiled. "Or, perhaps, the horse will learn to sing".
One of them was only wise when he was being paid by the word...