You cannot gain anything without first giving something in return.
In order to obtain, something of equal value must be lost.
Based off of the anime, Full Metal Alchemist, this thread is about the Law of Equivalent Trade.
Do you think that it exists in our world?
Don't just give examples on possible things that could happen to prove/disprove this theory. To make this more interesting, talk about your own personal past experiences that prove or disprove the law.