My favorite song from one of my all-time favorite movies (The Wizard of Oz), I think "Over the Rainbow" describes human nature perfectly. Think about it- we're always trying to reach for a dream of ours, but it always seems to be just beyond our grasp, somewhere in the clouds.
Humans can never be contented with what we have. We want to live in a world "where troubles melt like lemon drops way above the chimney tops".
Even though we'll never get there, we strive for it anyway. It appears simple.
'Cause it's just somewhere over the rainbow...