What event was the catalyst for O'Connell's son's epiphany about the role of the artist?

O'Connell describes in Chapter 6: Under the Hide the moment when his young son first recognized the concept of an artist's role. He was reading The Lorax to his young son and his son began to understand that the ideas coming out of the Lorax's mouth on the page were likely shared with the writer Dr. Seuss himself.