Dunbar’s number

Etymology

Named for the anthropologist Robin Dunbar, who in the 1990s correlated primate brain size with social group size and extrapolated a figure for humans. The exact number is debated; the useful part is the idea of a ceiling on real relationships.

noun · /DUN-barz NUM-ber/
The rough cognitive limit — often cited as about 150 — on the number of stable relationships a person can maintain.
What it names
Why organizations, group chats, and communities change character past a certain size — you can no longer actually know everyone.
Example
The company’s culture shifted the moment it blew past Dunbar’s number and strangers began filling the halls.
Related idea
Parasocial ties feel like they expand your circle, but they don’t count against Dunbar’s number — they’re one-sided.