When things are written down, they become laws. I've been in situations where I've been told that "you're not following the documented procedure." Reason for this was sometimes that I forgot, and sometimes it was because I thought that the documented procedure was not valid. Only thing is that in some of those situations I wrote that documented procedure. Of course, I've should've updated the documentation. But this shows how written word becomes the truth, something you cannot change.
This is one of the reasons why many software process implementations fail. They are following standardized process model, which they will follow blindly, even if they do not work on their situation.
When new process model or methodology emerges, innovators and Early Adopters usually understand the meaning and possibilities of new methodologies. They understand that the new thing might not work for them, and they are willing to try and able to modify it. Majority will check what innovators and early adopters have done, and then implement it like it's business as usual. And in this point, things will start to go downhill. Most of the majority will fail in implementation, because they wont adapt the methodology and process model.
While I was writing this post, I happened to read a blog post which was titled "How Good Becomes the Enemy of Great". It manages to say a lot more clearly what I'm trying to say here. There are no silver bullets, you must keep your eyes open and adapt to your own situation.