There's a phenomenon in which you see yourself in a department store mirror, and see the "self" you expect. But then another shopper appears in the glass, and in an instant you see your face very differently.
When you see your face in a social context, your mind can no longer apply whatever flattering "filters" it likes. The second person comes in like sudden, harsh lighting. Flint went a long time with no social context in the mirror, because Rayna was really just an extension of how he saw himself. She saw him through his eyes, as a unit built and programmed by him.
I once read a Kawabata novel where the protagonist sees his father in the subway window, then realizes he's seeing his own reflection! Of course, it's a comment on aging and how we perceive ourselves.
Not too many years after reading it, I experienced the same scenario on DC's Metro!