I've been thinking a lot about this recently. Magick is so similar to the placebo effect in medicine.
Magic is affected by things like emotions, thoughts, and beliefs, so is the placebo effect. Simply thinking about it can cause a change in it. Intensity of belief seems to be an important parameter for magic and placebo effects - when it comes to magick, the stronger you believe, the more potent it should theoretically be, and sometimes it can exist even if you don't believe in it, like how the placebo effect can occur even if you convince yourself that the "treatment" is not going to do anything and you already know it's "fake".
Placebo effects last for a short while only, same goes for magical phenomena. Magical healing similarly produces only transient effects, and is effective for minor ailments only (e.g. relieving psychosomatic pain). Neither magick nor the placebo effect can do literal miracles like cure cancer or regrow limbs etc.
It almost feels like magick IS the placebo effect, or at least only as strong as placebo. The "science of magick" then is really the science of placebo. Maybe that's simplifying it too much. Magick does exist independently as its own thing, or as a "separate world", you could say. It's separate from the medical placebo effect because it deals with more than just effects on the human body. Magic also deals with things like manifestation of external phenomena, external entities like "spirits", physical rituals and whatnot, that are seemingly beyond the scope of placebo related phenomena.
One should acknowledge, however, that since the practitioner's mind and its inner workings are subject to the placebo effect themselves, it means any and all magick done from the mind is subject to the laws of placebo as well. This would include "psychic magic", "law of attraction", "energy work" (with chi/prana/whatever). In fact, any form of magic can be explained by placebo-like effects because the mind (consciousness, subconscious, emotions, belief, etc) is responsible for creating these magical effects in the first place. No mind = no magic, after all.
Your thoughts?