"If you're going to show a fish out of his customary element, you first have to show him in that Ordinary World to create a vivid contrast with the strange new world he is about to enter."
It makes the audience understand the difference between the character's ordinary world and the new, strange world they will enter. If I, for example, watched the Harry Potter movies without seeing and knowing that Harry was from the "regular" human world, I would just assume that the wizarding world is his ordinary. I'd be confused as to why he would act so surprised and strangely over certain things.
The experiences of the preceding stages have led us, the audience, to identify with the hero and her fate. What happens to the hero happens to us. We are encouraged to experience the brink-of-death moment with her.
I agree that often when we watch movies or hear stories, if they are good stories, we will connect to the lead characters because we see something about them in ourselves. After taking both a film class and as we are working through this class, I find myself more and more amazed at the meanings behind plots and how the structures of these stories are built on. I see a lot of similarities in different kinds of movies, and the same goes for stories. The structures are often very similar, whether it's an action story or a romantic comedic story.
Roller coasters make their passengers feel as if they're going to die, and there's a great thrill that comes from brushing up against death and surviving it. You're never more alive than when you're looking death in the face.
I like how the author used a physical example to describe the emotions we can go through when reading a story. Although we may not feel the exact same feeling, it's somewhat what we imagine it to feel like when we read a story that we are emotionally invested in. The roller coaster can also symbolize the emotional journey that we go through as the story progresses. I imagine that people who are thrill seekers are the kind of people who enjoys roller coasters the most, along with other activities such as skydiving.