Another simple explanation: Imagine that there was one single person who was friends with all 7 billion people on Earth. Assuming nobody else had more than abo

Another simple explanation: Imagine that there was one single person who was friends with all 7 billion people on Earth. Assuming nobody else had more than about 250,000 friends, this would cause every other person on the planet to have fewer friends than their friends have, on average. That one person skews the mean. What happens in reality is of course much, much more subtle.