It was during one of these sessions with Aqua that you learned a little more about why most of the mares became guards. There was no conscription: all of them had volunteered for the job. Aqua herself came from a long line of guardsmares, going several generations, as far as Nightmare Moon's banishment, and a bit before that. Most of the other mares had similar stories as well, stating that Celestia was very picky about which ponies ended up in the Royal Guard, and very rarely accepted new lineages. Of course, from what Aqua said, the job is very boring and pays decently well, but there wasn't much else to do, with them being restricted to castle grounds, other than talking and reading books.