I remember back when I was younger, I was one of those kids who was likely a terror to my mom when it came to cleaning up after myself. It wasn’t until college when one of my semesters where I had a room-mate who was infinitely messier than I was that it finally struck me with that empathetic understanding of just how much of an aggravation I was to my mom. I expect that is like that with a lot of things where people never realize certain aspects of their own personality until they are struck in the face with it by someone else entirely.
I guess though the trick is recognizing it in yourself. Because truth be told I’ve seen a lot of folks react negatively to a trait in another person, never noticing that they themselves likely embody the thing they are chastising the other person for having.