Who you became friends with was decided by which door you happened to live near
In a 1950 study of a postwar student housing complex, Festinger, Schachter and Back mapped friendships and found physical distance mattered more than shared interests: people two doors apart were far more likely to become friends than people at opposite ends of the same hallway. Residents who lived near stairwells or mailboxes made disproportionately many friends, simply from being passed more often.