“Viral marketing depends on a high pass-along rate from person to person. If a large percentage of recipients forward something to a large number of friends, the overall growth snowballs very quickly. If the pass-along numbers get too low, the overall growth quickly fizzles.” marketingterms.com
Of course, virality is also a pre-condition for fake news. When ideas move fast—in their production, reception, or pass-along—we give up the time necessary for research, verification, contemplation, and action.