Tribes: the groups that already exist before your badge
Every company above a certain size splits by itself into smaller groups of roughly twenty to one hundred fifty people, who know each other by name, by shared history, and by inside nicknames. The authors call this a tribe, and it exists whether or not the org chart recognizes it.
The limit of one hundred fifty comes from a natural ceiling: beyond that, nobody can keep in their head the history of their relationship with everyone. That is why a company with five thousand employees does not have a single culture. It has dozens of tribes, each at its own stage.
Think of the break room crowd, the people who wait for the same bus after work, the department group chat. Nobody signed anything, but everyone already belongs to a tribe before they even memorize their badge number.
For the authors, a company's real culture is the sum of these small tribes, not the mission statement hanging on the lobby wall.
