The stranger is an element of the group itself, not unlike the poor and sundry 'inner enemies'—an element whose membership within the group involves both being outside it and confronting it.
If we believe in data structures, we must believe in independent (hence simultaneous) processing. For why else would we collect items within a structure? Why do we tolerate languages that give us the one without the other?
We are all alone, born alone, die alone, and—in spite of True Romance magazines—we shall all someday look back on our lives and see that, in spite of our company, we were alone the whole way.