This is the paradox: When you improve something, you change it in ways you couldn't have expected.
My favorite example of unintended consequences comes, weirdly enough, from the United States. In a speech to a criminology conference, Nancy G. Guerra, the director of the Institute for Global Studies at the University of Delaware, described a project where she held workshops with inner-city Latina teenagers, trying to prevent them from joining gangs. The program worked in that none of the girls committed any violence within six months of the workshops. But by the end of that time, they were all, each and every one, pregnant.