In a psychological experiment a person was shown a photograph of himself and then a reversed image of the same picture. Consistently the person preferred the reverse image simply because it was the image that he was used to seeing in the mirror.
Why is this important, well that kind of familiarity can also spill over at work. You can favour similar people, but beware great teams consist of diversity. Make sure you are not judging by the mirror, make sure you are judging by results and behaviour.