"You did not nail up your chest of buckskins when I refused to pay interest; the nature of your capital made you willing to continue the negotiations. Not so the money-capitalist; he would bang the door of his strong room before my face if I announced that I would pay no interest. Yet I do not need the money itself, I need it only to buy buckskins." (Gesell, A Story of Robinson Crusoe)
Even in the course of time money doesn't lose its worth, the natural threats do not concern money and the money-owner has the power to collect interest. This is why Gesell makes Robinson say in the end:
"For Marx money is simply a medium of exchange, but money does more, it seems, than ›merely pay the price of the commodities it purchases‹, as Marx asserted. When the borrower refuses to pay interest, the banker can close the door of his safe without experiencing any of the cares wich beset the owner of goods - that is the root of the matter." (Gesell, A Story of Robinson Crusoe)