. In his book Social Theory and Social Structure, he conceives of a bank run at the fictional Last National Bank, over which Cartwright Millingville presides. It is a typical bank, and Millingville has run it honestly and quite properly. As a result, like all banks, it has some liquid assets (cash), but most of its assets are invested in various ventures. Then one day, a large number of customers come to the bank at once—the exact reason is never made clear. Customers, seeing so many others at the bank, begin to worry. False rumours spread that something is wrong with the bank and more customers rush to the bank to try to get some of their money out while they still can. The number of customers at the bank increases, as does their annoyance and excitement, which in turn fuels the false rumours of the bank's insolvency and upcoming bankruptcy, causing more customers to come and try to withdraw their money. At the beginning of the day—the last one for Millingville's bank—the bank was not insolvent. But the rumour of insolvency caused a sudden demand of withdrawal of too many customers, which could not be answered, causing the bank to become insolvent and declare bankruptcy. Merton concludes this example with the following analysis:
The parable tells us that public definitions of a situation (prophecies or predictions) become an integral part of the situation and thus affect subsequent developments. This is peculiar to human affairs. It is not found in the world of nature, untouched by human hands. Predictions of the return of Halley's comet do not influence its orbit. But the rumoured insolvency of Millingville's bank did affect the actual outcome. The prophecy of collapse led to its own fulfilment.[3]
