He was worried because he thought that the windmill could be very difficult to make, or that it wouldn't work and he would have to live without purpose and any resources.
William wants to make a windmill for his community. He knows that this will be the biggest project of his life and that if it goes wrong, he will live without any purpose and that saddens him and makes him afraid.
More information about harness wind is at the link:
https://brainly.com/question/13892636