"Fullmetal Alchemist" Laws and Promises (TV Episode 2004) - Rie Kugimiya as Alphonse Elric

Alphonse Elric : 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 does not encompass everything that goes on here, but I still chose to believe in its principle: that all things do come at a price, that there's an end and a way, that the pain we work 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're expecting. I don't think of Equivalent Exchange as a law of the world any more. I think of it as a promise between my brother and me, a promise that someday we'll see each other again.
Alphonse Elric : In order to gain something, you must present something of equal value. That is the principle of Equivalent Trade. Back then, we had believed it to be the truth of the world. But as it turns out, the world is an imperfect place, and there is no principle that can explain its existence. Not even the principle of Equivalent Trade. But we still believe that one cannot gain something without paying the price. The pain we endured must have been the price for something else. We also believe that by paying the price of hard work, we can gain something. Equivalent Trade is not a principle of the world.

Rie Kugimiya: Alphonse Elric