Butterfly Effect

Jon suddenly had an idea. He had heard of the Butterfly Effect, where relatively small changes can ripple out to have large scale, long term consequences. Though he was sure that what constituted 'small' would likely vary from person to person, he decided to try it out. He would make a single, small (from his perspective, anyways) change and study how that change affected society on a larger scale as each change caused changes of their own. He would have to include a clause that would allow him to reverse the changes he made of course, as he couldn't necessarily predict all the changes that would result from his initial alteration. But what would he wish for, first?