Once a farmer found an abandoned eagle's nest and in it was an egg still warm. He took the egg back to his farm and laid it in the nest of one of his hens.
The egg hatched and the baby eagle grew up along with the other chickens.
It pecked about the farmyard, scrabbling for grain. It spent its life within the yard and rarely looked up. When it was very old, one day it lifted up its head and saw above it a wonderful sight - an eagle soaring high above in the sky. Looking at it, the old creature sighed and said to itself, "If only I'd been born an eagle".
Source: an adaptation from an Anthony de Mello story