David Brooks writes about how we find and keep friends, usually a maximum of about 150 friends.
Dunbar argues that it’s a matter of cognitive capacity. The average human mind can maintain about 150 stable relationships at any given moment. These 150 friends are the people you invite to your big events — the people you feel comfortably altruistic toward.
He also argues that most people have a circle of roughly 15 closer friends. These are your everyday social companions — the people you go to dinner and the movies with. Within that group there’s your most intimate circle, with roughly five friends. These are the people who are willing to give you unstinting emotional, physical and financial help in your time of need.