The idea was first explored by sociologist Stanley Milgram. We are actually connected with every single person in the world just via six people that know each other. So everyone is actually your friend’s friend’s friend’s friend’s friend’s friend.
https://www.linkedin.com/grp/post/25059-5799755194258436096

This suggests that the average path length of social networks around the world is small. Psychologist Stanley Milgram (link is external) did an experiment in the 1960s where he asked a number of people in the midwestern U.S. to send a letter to somebody in Boston. However, they did not receive the address of the person, but just a number of hints, like occupation. To reach their target, people had to send the letter to somebody they thought would have more success in finding the target. Milgram was interested in whether the letters would arrive at their target address, and how many connections it would take. Not all letters reached their target, but of those that reached the target the average number of links was six. This led to the saying that all people are on average just six handshakes away. This experiment was replicated 35 years later with emails, and again the average number of links between the source and the target was found to be six.
https://www.openabm.org/book/33102/114-small-world-networks
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