As I understand it, if you are moving fast enough relative to me, your mass increase will cause you to APPEAR like a black hole to me, even though you will not see yourself as a black hole. It would be an illusion, right? And also you would see me as a black hole while I would reject that view. Ok, so how do we know the same thing isn't happening in some way with a "real" black hole? Maybe a black hole only APPEARS to be a black hole when it's really not.