At school, a fancy one that my mother toiled to afford, we were reading "A Tree Grows in Brooklyn," Betty Smith's semi-autobiographical novel about a family fighting indigence and hard luck in early-twentieth-century Williamsburg. Francie Nolan, the teen-aged protagonist?"nerdy, plain, and secretly ambitious, like me?"loved the smell of coffee, one of the family's few luxuries, but she seldom drank her serving?""at the end of the meal, it went down the sink." It was Francie's mother's comment, in particular, that stayed with me: "I think it's good that people like us can waste something once in a while and get the feeling of how it would be to have lots of money and not have to worry about scrounging." Unlike Francie, though, I gulped down king-sized cups of boba without leaving behind a single drop. When only melting ice cubes remained, I hunted the last tapioca balls stranded among them as if on a search-and-rescue mission, and savored how their gummy vestige