Read the passage and answer the question. The tortoise wanted to attend a feast in the sky, but he had no wings. He begged the birds, and each bird lent him a feather. On the way, he told them that everyone at a feast takes a new name, and he chose the name 'All of you'. When the food was served, the hosts said it was for 'all of you', so the tortoise ate most of it. The angry birds took back their feathers, and the tortoise fell to the ground and cracked his shell. What lesson does the story teach?