When I was a wee lad, my mum insisted I always wear a helmet when going out on my bicycle. Many a time I argued, "forgot" and completely ignored my mum (it was a hideous looking thing - like a polystyrene bowl with a pair of knickers stretched over it to give it some colour), but eventually I reluctantly started wearing it, and now ALWAYS wear my helmet when out on my bike.
I was always under the impression my mum insisted I wear a helmet to protect my head in the event I was hit by a car, but as it turns out, it was to protect me from my own actions - a bit like a cork on the end of the fork. My helmet has actually saved my head and face from my own actions on several occasion. On one, I came off as I entered the driveway and flew into the gate. I've got the scar on my shoulder but thanks to my helmet, I don't have a scar on my head to go with it. It also saved my face when I hit a pothole at about 40kph and severely broke my right wrist. My face wouldn't be as beautiful as it is now had I not been wearing my road-buffer, I mean helmet on that day ;-) .
Now, I'm sure my mum heard many horror stories about what happens when you come off your bicycle without a helmet - she did work in a hospital for a long time - and I'm sure she pictured every one of them happening to me, but I bet she never imagined something like this happening to me...
I doubt Evan van der Spuy's (the guy clobbered by the red hatebees) mom imagined his helmet would come in handy in this event either.
So folks, this is why you must wear a helmet when riding your bicycle, and I don't care if you don't think you'll be getting any wild deer prancing through the streets of London. You never know :-D