Comment by Jerrrrry

I do not mean to discount this interesting iota, however, I had a similar realization when I was 7; whether it coinciding with learning of the Copernicus principle is merit or raw luck notwithstanding, I saw my siblings as none other than another family in another house: all others would view me, and us, as neighbors, and we are all side-characters in each others story.

That thought is "sonder" - although it differs from what you describe, it has some parallels.