Well this is an interesting question that goes back to the beginning of time.

Before banks, trading markets, and other mediated forms of exchange people would barter based on percieved value. A cow for 20 chickens, or something like that. The value of an item is whatever people decide it to be. Yes, exchanges help make the process easier, but it's just a means to an end.

If someone thinks your asset has value, they will give you something for it.