Lending is another topic, since it involves the risk of default. In your example, the car salesman would not trust a promise from a third party which he has no idea of credibility. Those 80 coins are not considered as money but a debt. Of course you could rely on large institutions, but risk of the failure of those institutions is still high, just look at how many bank failures during the financial crisis. Maybe the risk is very low under normal time, but when it fails the impact is enormous, so the average risk could be higher, you can not minimize the risk by moving them around, actually you increase the risk when you move all of them to a single point of failure

But let's put it aside and start with basics without involving lending. What RBD theory indicated has nothing to do with FRB, it is this part I am most interested in this thread