You know we humans have amazing balance.  We also are the only animals that know we're gonna die one day.  Which is why I can easily balance and run on a street curb with no problem...but put that sucker 5 or 10 feet up in the air(ala a balance beam) and I can barely take a step without falling.  It's because I understand the danger. 

So explain THIS guy.  On the edge of a cliff riding a dirt bike.  No thanks...I'll stick to riding my bike at the gym where I can watch TV while I surf the web from my Droid.  I don't want to die.