Eugene had gotten as shy as a hermit crab around people, especially women. Because he was unable to fly while someone was watching he couldn't prove he could do it and the jeers of his childhood rumbled like a truck in his mind.
Because he he couldn't fly with anyone watching, he couldn't tell them he could. He was the only one who could know it and the frustration of knowing that the one thing he did well would never be known nibbled at him like a mouse.