lonely v/s alone?

a lot of people i know find being alone daunting/intimidating/depressing/overwhelming... they need to be constantly around people to feel alive. i for one love solitude. i can be alone for hours, do nothing, and yet be completely occupied. that could be to some extent because i am constantly evaluating- people, places, situations, the tree in front of my window. so what makes some people so comfortable with themselves and others so terribly ill at ease when all alone?
some say "only" kids have this tendency to crave solitude. in fact, people beyond a point grate on their nerves. i can ascribe to that train of thought considering i am an only kid, yet, i think that being alone sometimes has tremendous advantages. not always but sometimes!
another thought that comes to mind is that we are fast becoming a world of single kid families, so are we on the brink of a generation that will constantly resent company that is below par?