An eagle’s egg

Get Rich Slow by Tama McAleese opens with the following preface, attributed to an unknown author.

A man found an eagle’s egg and put it in the nest of a backyard hen. The eagle hatched with the brood of chicks and grew up with them. All his life the eagle did what the backyard chickens did, thinking he was a backyard chicken. He scratched the earth for worms and insects. He clucked and cackled. And he would thrash his wings and fly a few feet into the air.
Years passed and the eagle grew very old. One day he saw a magnificent graceful majesty among the powerful wind currents, gliding with scarcely a beat of its strong wings. The old eagle looked up in awe.
“Who’s that?” he asked.
“That’s the eagle, the king of the birds,” said his neighbor. “He belongs to the sky. We belong to the earth. We’re chickens.”
So the eagle lived and died a chicken, for that’s what he thought he was.