What are friends for?” This isn’t a rhetorical question. Friendship is one of life’s most important features, and one too often taken for granted. The human desire for companionship may feel boundless, but research suggests that our social capital is finite—we can handle only so many relationships at one time. Social scientists have used a number of ingenious approaches to gauge the size of people’s social networks; these have returned estimates ranging from about 250 to abou