A question like that can hit you pretty hard when you are staring into a hotel mirror at some ungodly hour of the morning, after a sleepless night, about to make your first appearance on "Good Morning America." I know because this happened to me not long after I wrote a two-page magazine story coining the phrase "urban tribes.'' For reasons that were never made entirely clear, the producers thought I was a generational expert who could explain why the number of "never-marrieds'' had more than doubled in a single generation. Who were these people who were delaying marriage, they wanted to know, and what were they doing with their lives? I had been flown to New York to summarize the lifestyles and life choices of 37 million youngish Americans.