Real assets typically have a use value and an exchange value. Even if you can't sell such an asset (meaning it has no exchange value), you can still profit from it by using or consuming it (it does have use value). Fiat money, including crypto-currencies, are pretty special in this regard in that they only have exchange value, and no use value.
Real world currency's value comes from an entire nation requiring it be usable for debt. That's an incredibly value thing to have. Cryptocurrencies have no such backing, and rely entirely on speculation for value.
Every day people say this as if it's a new insight.
There are many things that are valuable that don't derive that value from some other asset "backing" it.
Money is a social construct that is valuable because people agree it's valuable. When people decide it's no longer valuable, then it's not.