Just before the year 1000, a rumor arose in a certain town in Germany, Hamelin I believe, that the coming of the new time would bring rats to the public buildings. Some had been spotted in the basement of the town hall, some in the local stables. Rat preventers were hired at great price, and indeed when the century turned no rats were to be seen.
The city fathers felt shamed by the scare and called the preventers before them. You have spent a great deal of money on these rats ? but there were no rats, they said.
Ah, city fathers, said the preventers. That's because we prevented them.