Six degrees of separation

Through just five or six intermediaries, you could be linked to millions of others. It is the notion behind what has been dubbed the small world effect. Robert Matthews explains how the theory affects us

The article explains the experiments conducted by The US psychologist Stanley Milgram. It then goes on to explain the various conclusions from this and in the section They're everywhere the various examples of this rather bizzarre fact is used in movie business

The world of showbiz is now recognised as a classic small world.
That is, it is made up of lots of little cliques of actors, most of whom
stay in their own patch of the industry, mixed in with a few highly
versatile ones with random links right across the acting network ­
who thus link every actor to every other via very few steps.

and the "Germany's biggest firms actually form a cosy small world.".