In some city an amount of people injured in car accidents was very high. Then it was decided by administration to make the using of seat belts oblidatory. People started to obey this rule. But the amount of crash accidents remained the same. Moreover, the number of injured people who addressed to the hospital even increased.
The adopted law decreased the number of accidents. A lot of people who would die without seat belt stayed alive but got injured and therefore they went to the hospital. So the number of patients increased.