The boy Michelangelo had never carved a figure.
He asked the old teacher in Lorenzo De Medici’s garden-school for a chisel and a piece of marble. He especially liked one of the antique marbles in Lorenzo’s collection, the head of an old faun, and he wanted to try to copy it.

Detail of a faun from a first-century BC marble sculpture group now in the National Museum of Athens

When it was finished, he proudly showed his faun to the Duke—propped it up in the garden so that the Duke would be sure to discover it as he strolled through one morning.
And when he saw it he was really amazed. It was a perfect copy and an astonishing achievement for a boy who had never carved before.

Lorenzo de Medici by Angelo Bronzino

But then, just to tease Michelangelo a bit, the Duke told him there was one big error, did he know what it was. Michelangelo shook his head, crushed, angry at himself for the obvious error, whatever it was, angry at the Duke for smiling at it. “That’s an old faun,” said the Duke. “And an old faun wouldn’t look that good. He would probably have a few teeth missing, don’t you think? And the others would be worn down from all the years of chewing. But otherwise, your faun is very nice.”

Michelangelo couldn’t allow that mistake to stand forever in stone for everyone to see and grin at like the Duke; and as soon as he could—secretly, perhaps by night—he corrected it, chipping out a couple of the faun’s teeth and digging holes in the gums. Later, when the Duke noticed the changes and that Michelangelo had taken so seriously his teasing—in childish simplicity, as he thought—he found the whole thing charming and told the story over and over again to his friends.