As best I can tell there is a well described reality, and that reality constrains what is not only probable, but what is possible. Within the limitations of our current understanding of reality, some processes are impossible, i.e. have zero prior probability.There are a couple of important points in this so lets break it down a bit. The first assumption is that there is a reality outside of us. "Reality is that which when you stop believing in it, doesn't go away", I think the quote is, Philip K Dick if I recall correctly. If you don't agree with this base assumption, or are going to insist on getting pointlessly philosophical, then quite frankly, go away, there is no point in me talking to you.
If you accept that there does exist an external reality, then the next thing to not is that this reality does not let anything happen. Anything is possible is patently untrue, even in an infinite universe. I would go so far as to not get to picky when people say that in an infinite universe everything that can happen will happen, though I think even that is debatable. Easily debatable. If it is possible for something to happen once or continually, in an infinite universe, it is also a possibility that it will never happen. These things are mutually exclusive.
Anyway, that's not the important bit. The important bit is the second half of the quote. We don't know everything. Dara O'Brien said it well when he said that "Science knows it doesn't know everything. If it did, it would stop". The flip side of this statement is not mean that whatever theory some crackpot comes up with can be true. Technically we might be limited by our current understanding of the universe, but we've been at this figuring shit out thing for a while now and while we can always refine our understanding, we do understand some things quite well. If someone wants their pet theory to be true they must show that either it is plausible within our current understanding of reality or that our current understanding of reality is incorrect or limited. And proving that second one, is hard. Really hard. You have to have some pretty spectacular data to back up claims that show current understanding is wrong. So things like applied kinesiology, homoeopathy, reiki and astrology etc., which are not plausible within the limitations of our current understanding of reality (i.e. given what we know, have plausibility zero) would need to come up with some pretty spectacular data to show that they do work. And given that the only effectiveness any of those things have is no better than placebo, then given what we know, it's very very easy to dismiss them.