I don't think you're taking someone's loss, the market perception of the value of the commodity/crypto is what's changing, your just taking from the pool of everyone's money that bought, that pool isn't infinite, it relies on people buying and holding, if everyone wanted to sell or cash out at once, the commodity/crypto would become worthless and the pool of money would eventually be illiquid and run out, and almost everyone would lose all the money they put in because the pool is only as big the circulating supply times the perceived value. So everyone's just betting on it being stable enough to hold value essentially, at least thats what I figured after I thought about it for a bit.