Sets And Subsets

Second post of the day:
It occurred to me that there are innumerable sets and subsets, and sub/sub/subsets among humans.  This thought was triggered by viewing the Westminster Choir College Barbershop Quartet on YouTube singing one of my favorites, Bridge Over Troubled Waters.  That group is a subset of music students at Westminster, and both are sub/subsets of the overall music community.  Runners are another subset--say, of fitness enthusiasts, which may also include weight lifters, Olympic athletes, and vegetarians.  There's theatre, of which I'm happy and proud to be in the tiniest, teeniest, minuscule part.  There's education, from Ph.D.'s to a guy teaching auto repair to his nephew in the garage and--oh, so many others.
I'm a member of more: motherhood of the parent set; multiple birth, as a twin; readers and under that, one of those with a preference for non-fiction; the elderl...uh, olde...that is, over 55 subset, which I guess can be divided into every age there is.  Oh, of course, there's a lot more to me: those who went to Holy Spirit High School, who are pacifists, who are half German and half Irish (the most common ethnic mix in the United States), who prefer dark meat to light on Thanksgiving.
I'm not sure why, but it's somehow comforting to identify your "sets."  For instance, when I'm in a new place for any length of time and I happen to visit a college or university, I feel at home.  I'm used to them, I know about their cafeterias and the problem employees and why the Admissions Office is so much more inviting than Facilities Management.
Same with shore places.  Even in Singapore, though its ocean is not the one whose waves I heard through my childhood, I recognize the color and the shells and the sand on its border.  Of course, my subset is the Jersey shore and within that, Ventnor, and after that, Rosborough Avenue, and then that room on the second floor to the left of the staircase...
Okay, philosophising over!