Most of us have experienced one of our best solutions backfiring and unintentionally creating a bigger problem in the future. One historical example of an unintended consequence occurred in the early 1900s in Hanoi, Vietnam. Under French Colonial rule, the city was proud of the sanitation benefits of its indoor toilets supported by a vast sewer system. Soon, however, rats gravitated to the underground network of pipes and began to proliferate wildly. In an effort to reduce the exploding rat population, health authorities embarked on the Great Hanoi Rat Massacre.
Civilians were paid a bounty for each rat they killed. In order to reduce the space needed for entire corpses, only the severed rat tail was required for payment. While the rat population decreased initially, large numbers of tail-less rats suddenly appeared on the streets. It turned out that rat hunters simply cut off the tails, received their payment, and released the rats for further breeding and tail-making. Even worse, health inspectors discovered new farms on the outskirts of Hanoi dedicated to importing and breeding rats.