美国2009 年很流行的黑色幽默“小镇上的100美元”:

It's raining and the town seems totally forgotten by people. It's a toughtime and everybody is in debt. All of a sudden, a rich tourist comes. He enters the only hotel there, lays a 100dollar bill on the reception desk,and goes to check the rooms upstairs in order to pick one from them. The hotel manager takes the 100 dollar bill and runs immediately to pay his debt to the butcher. The butcher takes the 100dollar bill and runs immediately to pay his debt to the pigraiser. The pig raiser takes the 100 dollar bill and runs immediately to pay his debt to the supplier of his fuel. The supplier of his fuel takes the 100dollar bill and runs immediately to pay his debt to the prostitute who gave him "service" before. The prostitute runs immediately to the hotel and pays off her debt with the 100dollar bill to the hotel manager to pay for the rooms that she rented when she brought her customers there. The hotel manager then lays the 100 dollar bill back on the desk so that the rich tourist will not doubt anything. At that moment, the rich tourist comes down after checking the rooms, and takes away his 100 dollar bill, saying that he does not like any of the rooms, then leaves. No one has earned anything. However, the whole town is now without debt, and looks to the future with a lot of optimism. And that's still how America does business in 2009.

    区区5 个当事人，已经令得简单的物物（债债）交换无法达成，可见交易成本的增长是多么迅速，“一般等价物”（货币的本质属性）是多么重要。那么交易（特别是金融交易）的另一种润滑剂-信用-能不能发展出类似的“一般等价物”，是个重要的问题！也许担保公司、保险公司、金融工程（可以分散部分风险）等的出现就有这个目的。

“小镇上的100美元”这个故事让我切实感受到了金融学的魅力。金融学最大的作用是价值的跨时间转移和风险的跨空间转移约束下的效用最大化。故事中游人的一百美元在小镇几经转手，最后完整地回到游者手中，但这100美元在其转手过程中就体现了价值的跨时间转移和风险的跨空间转移，并且最终实现了效用的最大化。游人最后没有花销却解决了小镇里连带的借贷关系， 这里就表现出社会生活中密切联系的借贷关系网。其中借贷关系的实现也表现为一种相互信任，并由此可以看出信用在金融活动中不可或缺的重要性。