In my dad's generation, it was popularized by the saying "now you've shook the hand of a man who has shook the hand of John L. Sullivan".

I was very aware of the six degrees idea in the 1970's and 80's when I was shaking the hands of celebrities who had shook the hand of presidents who had shook the hand of world leaders. And when I was 18, I worked for our Congressional Delegation, men who had all shook the hand of...