Teenagers

I know I am not the first parent to think this and I almost certainly will not be the last, but why do teenagers either think they know it all, think their friends know it all or think their teachers, at least I was told this spotty geek fresh out of teacher training college was a fully fledged teacher, know it all? I know when I was a teenager I thought I knew it all and my fuddy duddy Dad who had a sensible 9-5 job didn't have a clue about the real world in the 80's, but then that was the 80's, and my Dad was a bit fuddy duddy, this is the 21st century man and I ain't in any way fuddy duddy, am I? Now to let the thought that I might in some small way be considered fuddy duddy is a little bit like admitting that I am getting old & at 43 there is no way I am ready to admit to that, so I return to my original question of why do teenagers think they know best, sigh.