150 is about as large a group of people as the human brain can handle in personal relationships, notes a British military commentator Tom Ricks for Task & Purpose.
The story of the importance of stories begins not in leadership, but in anthropology. Robin Dunbar is a British anthropologist, evolutionary psychologist and a specialist in primate behaviour. In the 1990s he identified a correlation between the size of the pre-frontal cortex in ape species and the size of the social groups each species could maintain. If you took the size of an ape’s brain, you could calculate the size of its social group size. This number – the maximum social group size for a given species, based on pre-frontal cortex size – became known as the Dunbar Number.
Hence the limit on the size of an infantry company, he says, as well as on Stone Age farming villages and new religious sects.