We have only one or two true friends. But, we have many friends or “friends of friends”. The true friend is what we called strong ties. “Friends” or “friends of friends” is what we called “weak ties.” While true friend are always there to help us, friends are more flexible. 

How many friends can we maintain? According to British anthropologist Robin Dunbar, the “magic number” is 150. Dunbar became convinced that there was a ratio between brain sizes and group sizes through his studies of non-human primates.

How about friends of friends? The number can be unlimited. Because, Milgram found that we are connected to anybody in the world by maximum six degree separation.

What makes these research great? The researcher is creative. He can provide powerful evidences to support his theories. The idea of degree separation among human itself it’s not new. But, before this research, it is mostly debated in mathematics, not in social science..