Personally, I think the human mind is incredibly powerful- more so than most of us give it credit for- and a lot of what we may think is the result of witchcraft, magic or supernatural entities, is simply our minds responding to themselves or responding to our bodies or environments in a way that sort of makes things seem to happen or, on a personal level, actually makes things happen. I don't feel as though I will ever be confident enough to say, with certainty, whether or not things like the power of witchcraft actually exist as I don't think humans know enough about the world we live in, but I do think most of it is sort of just our own brains.
For the most part, I agree with Sherily. The brain is powerful, but also limited in it's understanding and capacities.
A lot of witchcraft stems from psychology as well, and you’ll notice this from a fair amount of research. It can be a spiritual journey to some, and it can be a therapeutic method to others, as everyone’s “craft” so to speak is different.