Sometimes I have trouble associating names with faces but I'm not as bad as Oliver Sacks, a British neurologist and author, who can't recognise any face, including his own. Scientifically speaking, Sacks suffers from a disorder called prosopagnosia, which is a disorder of face perception where the ability to recognise faces is impaired.
In the video, Sacks comically tells a story about how he assumes he's looking into a mirror when any old man with a beard is in front of him. Worth watching, just to see how the disorder affects him. [BoingBoing]