Richard F. Shepard, as keen and joyful a chronicler of New York as ever graced the pages of The Times, had simple advice for anyone out and about on the city streets. Look up, he said. Look especially at second-floor windows above storefronts. That, he liked to say, is where a lot of absorbing action takes place. Why would a perambulating soul wish to miss any of it?

One can imagine Mr. Shepard shaking his head at many of today’s New Yorkers. He died in 1998, so he never held an iPhone or, I’m willing to bet, any of its forerunners. But there’s little question that he would have found something hollow about this smartphone age, when so many people routinely violate the Shepard rule, New Yorkers being no exception. At any given moment, thousands of them are so focused on their little screens that they fail to look up. Truly, they don’t know what they’re missing.