The Hero as the Problem
Another truism from Worlds of Wonder is that the hero is also the problem. The conflict in a story is generated by the hero’s refusal to adapt; once the hero transmutes himself (in sci-fi often literally), the story is over except for the last bit of kick-boxing. Gerrold gives Luke Skywalker as an example of the transmuted hero (farmer boy to Jedi knight). Neo in the original Matrix would be a more up-to-date version.
I almost bought that chapter of the book, I admit, until I asked myself whether all stories were really that way. I’d say not. Some heroes never change - the stock characters of the pulps come immediately to mind. Some heroes change in a way that does not affect the plot; for example, Frodo finds he can’t go home again, though there had been no moment of decision at which he broke with his hobbit past. In some stories the point is that the hero remained faithful to what he was before, rather than breaking under external pressure - for example, Faramir or Howard Roark.
Overall, I’d say Worlds of Wonder is a good source of writing exercises and truisms, but next time, I’m reading The Art of Fiction.