Equivalent Exchange - Law of Alchemy

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. In those days, we really believed that to be the world's one, and only, truth

But the world isn't perfect, and the law is incomplete. Equivalent Exchange doesn't
encompass everything that goes on here. But I still choose to believe in its principle: that
all things do come at a price. That there's an ebb, and a flow, a cycle. That the pain we
went through did have a reward and that anyone who's determined and perseveres will
get something of value in return, even if it's not what they expected
~ Alphonse Eric, Full Metal Alchemist