Ninjas are the epitome of stealth. Can you think of anyone more stealthy than a ninja? Probably not. If you think you can, then why don't you just say that to the ninja that just snuck up behind you. Just kidding! There's no ninja there. Unless this was some kind of weird coincidence. Then again, we can't be certain there is no ninja there. They might be there, with you right now. And you can't see them because they are just too stealthy.