A while back, I was talking with a teenage girl about her privacy settings and noticed that she had made lots of content available to friends-of-friends. I asked her if she made her content available to her mother. She responded with, “of course not!” I had noticed that she had listed her aunt as a friend of hers and so I surfed with her to her aunt’s page and pointed out that her mother was a friend of her aunt, thus a friend-of-a-friend. She was horrified. It had never dawned on her that her mother might be included in that grouping. Over and over again, I find that people’s mental model of who can see what doesn’t match up with reality.