I recently started working with someone who wanted to rework an in-progress novel to very rigidly follow the three act structure and elements of the Hero's Journey. I realized when it was pointed out to me that the my other collaborator and I hadn't really been following the three act structure, but I thought this was fine. Even when I agreed to rework things, I was surprised at the near-total rewrite they wanted and their refusal to subvert any of the steps they had learned. We've since talked and agreed to find more of a medium, but this did raise an interesting question for me: How important is the three act structure?

Is it vital for a successful story? Can you bend it without breaking it? There are myriad other questions this raises, and I wanted to get the communities opinions.