One day, when my father was still in his 20s, he was walking in Berlin, and upon coming across a man in an overcoat thought to himself "it's funny, this man has exactly the same coat as my brother!" - it turned out it was his brother...
Welcome to the world of prosopagnosia, also known as face blindness.
It seems like such a weird condition - after all, life is based on us recognising the people we know!
Indeed, for those of us who suffer from it, life can be quite a challenge, as everyone seems to take "being recognised" for granted.
The way it works, or rather doesn't work, is that the bit in the brain which normally puts all the details of a person's face together to form a meaningful picture, doesn't do that job, or at least not properly. When babies are small, they can even distinguish between faces of monkeys. By the time they are about one year old, the brain cuts away all the "useless" capabilities.
Think of it as when you see people of a different race to yours - and you struggle to tell them apart. The whole "white/black/Asian people all look the same" is a way for our brains to do only what is necessary for them - and unfortunately for face blind people, that pruning inside our brain just went that little bit too far...
I suffer from face blindness, though possibly not at the same degree than my father.
I will come across the same people multiple times, and unless I have a relationship with them, or they have unforgettable features, I will not recognise them...
I will remember your clothes, your glasses, your eyes, your nose, your hair style, but not your face as a whole. It's harder for me to recognise "pretty" people, as they tend to have less prominent features. And if you change your glasses or your hairstyle, I may get that niggling feeling that I may know you, but I won't recognise your face.
One of the hardest challenges for me is when one of my children changes schools. It means a whole lot of new faces that I cannot recognise. My trick to try and avoid offending people is to smile widely and say hello to literally every single person at the school, in the hope that this way I won't offend the people I have met before but don't know that I know...
Very often I will introduce myself to people only to find out that I have actually met them before - but they remember very well that I did, and though I will definitely remember the conversation I will not know I had it with that person in particular.
A famous example of a completely face blind person is the psychiatrist Oliver Sacks - Bill Hayes (his partner) described it very movingly in his book Insomniac City (book I wholeheartedly recommend by the way) - how Sacks would stand next to a person at a function who happened to be about the same height and build of Hayes, and wearing vaguely similar clothes, and asking that person about their weekend plans, fully convinced he was talking to his partner...
When I read that, or think about my father, I realise I am not that badly afflicted. Faces do imprint themselves in my brain after a long enough time. I recognise my family, and my friends that I have spent a lot of time with. Clients can be tricky, as I do recognise them in my office (they tend to match the names in my diary lol), but I definitely don't when I bump into them at the supermarket; but I think that is a rather good thing - who wants to be greeted by their therapist in public anyway!
So please, if I ever see you (especially out of context) and ignore you, don't assume it is arrogance or carelessness, but rather blame my prosopagnosia :)