Count how many ponies there are. I guarantee you that the majority of them have had anywhere from two seconds to five minutes in actual show canon.
I also guarantee that each and every one has been named; each one has a story written about them. For each and every one, there is a headcanon.
Example time: Look to the far right, where there is a grey pony, playing cello while being harassed by a white unicorn with a blue mane. Between the two of them, they have perhaps a total of five minutes of canon screen time, including the show promo "Equestria Girls."
The fandom has decided that they are named, respectively, Octavia and Vinyl Scratch. They both live in Canterlot, working jobs as a cellist and DJ, respectively. (DJ-P0N3 is Vinyl's DJ tag, and is actually ascended fanon at this point.) Depending on whom you ask, they are good friends, roommates, or caustic lovers.
Like I said, you have no idea.