When I was younger I decided that, if forced to wish something, I would wish for all children (starting with those born at the moment I was wishing) who would be unable to afford dental or orthodontic care during their lives to have naturally strong, straight teeth. This could save them a lot of pain and health problems, while not negatively impacting the livelihoods of dentists and orthodontists. Also, I figured that the matter of dental problems was inconsequential enough that it wouldn't throw things off too much. I distinctly remember saying to my parents, "It's the best wish!" (Of course, not wishing anything was preferable. This was just the only thing I could come up with that would have a benign effect while having relatively little impact.)
In hindsight, that wish was really weird. 
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"No man is an island, entire of itself; every man is a piece of the continent, a part of the main. If a clod be washed away by the sea, Europe is the less...any man's death diminishes me, because I am involved in mankind..."