Dunbar's Number
"Humans can maintain about 150 stable relationships"
Origin: Robin Dunbar's research correlating primate neocortex size with social group size (1992)
The Key Insight
Dunbar's number isn't a limit to accept - it's a constraint to design around. Biology shows many solutions: hierarchy, modularity, specialized communication channels, and distributed decision-making.
What People Think
A hard limit on meaningful relationships. Once your company exceeds 150 people, you need formal structures because informal coordination breaks down.
The Deeper Truth
Dunbar's number is actually a scaling law about coordination costs. As groups grow, the number of potential relationships grows quadratically (n × (n-1) / 2). With 150 people, that's 11,175 potential relationships to track. The brain simply can't maintain that many. But 150 isn't a cliff - it's part of a fractal pattern: ~5 intimate friends, ~15 close friends, ~50 good friends, ~150 casual friends, ~500 acquaintances.
Biological Parallel
Every social species faces this tradeoff. Ant colonies solve it through chemical signaling and specialized castes rather than individual recognition. Bee colonies use the 'waggle dance' for coordination without central planning. Larger organisms don't just have more cells - they have different organizational architectures (nervous systems, hormonal signaling, hierarchical structure).
Business Application
Explains why companies change qualitatively around 150 people - you shift from 'everyone knows everyone' to needing formal processes, org charts, and explicit communication channels. But the insight goes deeper: effective organizations create modular structures that keep working groups below coordination limits while connecting them through well-defined interfaces.
When It Breaks Down
The specific number 150 is an average with significant variance based on individual cognitive capacity and the 'bandwidth' of relationships (digital tools can extend weak ties but not strong ones). More importantly, organizations can exceed 150 through structural solutions - the question isn't 'how do I stay small?' but 'how do I scale coordination?'