What is the significant experience that occurs for William in Chapter 2? What impacts did it have on him?

In Chapter Two, after William's father built their house, he was able to spend more time on his own, during which, he allowed his imagination to take flight. William describes how, at one point, he was desperate for physical power after being bullied. As a result, he allowed himself to be treated by magical means, which were supposedly guaranteed to increase his strength. The magic, however fails, and William is humiliated in a fight. William then notes that this occasion was his "first and only experience with magic."