150 is not the optimal group size, nor the maximum group size.
150 is the number of people, according to Robert Dunbar, you can sustain meaningful relationships with at any given time.
People misuse this number. It doesn’t mean you can have 150 good friends in an online community. It means you can sustain a maximum of 150 meaningful relationships in your life.
After you’ve tallied up your family, college buddies, work colleagues and other associates, you don’t have many vacancies left for friends. But it gets worse. The true number is probably much lower than 150, perhaps as low as 60.
You’re not just fighting for a share of your members’ time, you’re fighting for a share of their friends. It’s easier than ever to interact, but we’re not interacting with many more people just because we can. Stimulating interactions is futile without securing some of those friendship slots.
Real friendships still involve real stuff happening. The best way to facilitate friendships is by stimulating shared events, emotional experiences, self-disclosure and reciprocity.