If you want to buy something and the guy says "I'd love to sell that to you, but your $100 was stolen in a bank robbery two years ago and it's on a list with its serial number"... well, that $100 isn't fungible, is it? Has little to do with the association, it's not you, it's the money itself. That said, my example is one that proves this happens for cash too. Extreme corner cases are funny like that.