Gilbert, the flightless goose, is based on a real goose who lived on a lake in Columbus, Ohio. The goose was like all the other geese in the pond, until it was in a terrible accident. After being hit by a car, the goose had to adapt to life on the ground. He was unable to fly, but he was able to adjust to his situation and live a good life.
Eric and Nataliya Goodman lived on that pond and watched from their window as the goose struggled and prevailed. When the goose was left behind by the other geese during the winter, they fed it. Other neighbors took care of it as well.
For all we know, the flightless goose may still be alive today.