These are a few things that cross my mind every time I see these guys.
1) they work efficiently and quickly.
2) they walk with purpose and work with determination.
3) they don’t let foolishness (or fools) get in their way
4) they are strong of body, spirit and will
5) they aren’t concerned with self-actualization, rather, they realize that their lack of formal education means that this is their lot and if they work hard perhaps their children will receive a better education and their families will be better off.
6) they have what to be proud of but are unassuming and humble.
7) of all the custodians in the world, they were zoche to serve in the Rebbe’s shul, maybe there’s something to it.
Extra Credit: They sometimes answer to kaddish, kedusha, borchu, and chazoras hashatz.