Principle of Rebound

Though not magical, when an alchemist performs alchemy the forces they are manipulating are not believed to be wholly human in origin-- but rather, of the Universe as a whole. Therefore, the consequences for attempting to bypass the Law of Equivalent Exchange are not limited to mere failure and cessation of activity. When too much is attempted out of too little, what occurs is called a Rebound, in which the alchemical forces that are thrown out of balance on either side of the equation fluctuate wildly of their own accord in order to stabilize themselves... taking or giving more than what was intended in often unpredictable and catastrophic ways, leading to accidental mutation, serious injury, or death.