Humankind cannot gain anything without first giving
something in return. To obtain, something of equal value must be
lost. That is Alchemy's First
Law of Equivalent Exchange.
"Alchemy: the science of understanding the structure of matter, breaking it down, then reconstructing it as something else. It can even make
gold from lead. But alchemy is a science so it must follow the natural laws: to create, something of equal value must be
lost. This is the principal of equivalent exchange. But I learned that night that some things cannot be measured on a simple scale. My brother and I knew the laws of science, of equivalent exchange. The
game required sacrifice, that something had to be taken from
us, but we thought there was
nothing more we could loose....We were wrong."
~Edward Elric (Fullmetal Alchemist)