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I've seen some configuration of the same 20-30 people on my commute to and from work for several years. None of us acknowledge any of the others, none of us know anything about one another (presumably), one of us could disappear one day and maybe at some point several months later someone else will briefly think, hey, wonder what happened to that guy, kinda like how you suddenly notice that a restaurant you use to pass by all the time has been a Foot Locker for the past year.