Human beings have been craving adrenaline since the first caveman dared the first lion to "catch me if you can." That's not to say that we all crave danger, but it's so much a part of our DNA that if we don't chase those thrills ourselves, we enjoy watching other people do it. If we didn't, YouTube probably wouldn't exist. But the awful truth about daredevils and their envelope-pushing stunts is that one day, their luck will run out, tragedy will strike, and loved ones will have to pay the price. Here are a few