that followed. sadly familiar, yet very different. the big data error, the social media error, all aspects of that new world that was nonexistent even on 9/11. all of that came into play. during this event. reporter: this sunday morning, looking back on the past week s extraordinary events in boston. osgood: in the wake of a sudden catastrophic event, people are often haunted by thoughts of if only powerful feelings of regret over things we always meant to do and say but always thought there would be another chance. that sense of nevermore was felt all too often this past week. lee cowan will be talking about it. (screaming). reporter: it wasn t just boston. there was another deadly explosion in west, texas. leaving friends and family without a chance to say good-bye. you know, just because someone leaves our lives, it doesn t mean that all of the feelings and the emotions and the things that we want to say them leave too. they just don t disappear. reporter: un