Do you ever see strangers and think I probably will never in my life see them again?

Just asked my family and they don't understand what I mean .it could happen anywhere on the street, in a shop , in a park anywhere someone walks past and I think I probably won't ever see you again in my life .Hard to explore but sort of their lives will go on all the ups and downs, relationships and jobs .It's kind of like the vastness of it all

Anyone understand what I mean?