We become antisocial because then we are happy with the thing we've got; the thing we've got in our heads; something that doesn't exist. A sad thought, knowing that in that moment you can be alive and do something that's worthy of your time. And we have but a short amount of time given.
The point is - we are never truly happy with ourselves and our life - there is always something missing. Even though your whole life is full of joyful and happy memories, there will always be a gap. It's something that drives us. It seems that no life is full filled without something missing in it. And that makes life utterly sad; to know that some people have everything but are not satisfied while some have nothing but see the beauty in everything. Now those people are beautiful and know how to make their life worth living.
“It does not do to dwell on dreams and forget to live.” - Albus Dumbledore