I never could figure out or understand what in the world was allowing those great shredder guitar players to play as fast as they did.  I knew that there were some tricks that a few of them had.  But how were they picking as fast as they were without messing up.  I then came to find out about alternate picking and how that style of picking allows for the maximum speed.  Not only that, but the more that you practice the more accurate you become with this kind of style.  I was very impressed the first time that I saw it up close.