Why did the ugly duckling become a white swan?

The ugly duckling turned out to be a swan. If he doesn't work hard, he will lose the white swan. It will get smaller and smaller, and it will always be black and ugly. Everyone said she was ugly, that is, he didn't work hard, so he lost the white swan. People laughed at her and said she was ugly. She felt that others laughed at him and bullied her. As a result, he will slowly work hard and become a white swan.