There are many flavors of friendship. Most people have situation-specific friendships, like with gym buddies or work pals, that may come and go, as well as a handful of close friends they know deeply. But rarest of all are the true forever best friends who are there for decades on end, through jobs, moves, relationships, fights, losses, and life stages.
What makes a friendship durable enough to get to that level? Shared traits, interests, and backgrounds help, says Robin Dunbar, an evolutionary psychologist and author of Friends: Understanding the Power of Our Most Important Relationships. Dunbar’s work suggests there are seven areas of overlap that are crucial: speaking the same language, growing up in the same area, having similar career trajectories, and sharing hobbies, viewpoints, senses of humor, and…