“Making it so an individual tweet’s publicness can be toggled on or off might help users feel more comfortable spending time there. And pushing new users toward secret accounts that can toggle individual tweets public might even allay some of their fears.   Or maybe nothing can be done. No one promises growth forever. Communities and companies of all sizes fall apart. And some institutions that thrive on their tensions for many years can one day find them exhausted, worn out, limp, their continued use driven more by convenience and habit than by vibrancy and vigor.”