Why is it so Important to fit in?

We all like to think of ourselves as independent, think for ourselves kind of gal/guy, so why do we work so hard to fit in?

I just read an article by Steve Carell in which he says he has finally come to terms with his uncoolness.  He accepted that part of himself is just a nerd, and not part of the in-crowd.  Reading that gave me pause to question myself and wonder; why is it so important to fit into a crowd?  Especially the 'in crowd'.  As if they had some secret answer to life itself.  Does food tasted better with them, clothes looked better, was sex better, all was answered inside this quest for acceptance by the cool people?

Most of us had some kind of High School trauma associated with being found out to be 'not cool' or unacceptable by the cool folks.  Why is that?  When so much value is placed on being separate, an individual, rugged, having our own thoughts? 

On the flip side, I've met a few individuals that considered themselves 'individualistic' and, quite frankly they were hard to spend any amount of time with. 

What do you see?  What is your take on this?  I would love to hear your point of view.