Elevators… Mostly have small spaces, and they travel in one direction at a time, upwards or downwards. Often used to describe our relationships in closed spaces.
I saw a TedTalk recently where the researcher looked at urban tribes with particular illnesses and their geographic clusters. It highlighted the impact our social networks have on our health.
In simple terms, a person with cancer is more likely to have close friends with cancer within their network. This held true for contagious, non-contagious or hereditary diseases.
Healthy people also had healthy friends.