Speaking about beliefs, how can anyone be a 'true believer' in anything in our industry? :) Just trying to define what Agile actually is will derail any discussion.
I 'believe' in common sense and competent people (at all levels, not just developers!) -- they can do it with waterfall just as good as they can do it with Agile (whatever that means!) or any other method. In fact, they will do it without any strictly defined method. They'll just do it as they have been doing it for decades.
Yes, we all know that 80% of all software projects end up in tears (which is actually consistent with the rest of the Universe so it's hardly a shocking or unusual statistic -- why should we be different from everybody else?), but obviously in 20% of cases people were getting it right :) Must be people and not the method which did the trick.