Just going to add a point here that I've mentioned a few times before.

You do not have to hit your head to get a concussion. A helmet will not protect you from such. You don't even have to hit your head. I found this out the hard way in a auto crash. I dismissed the police officer's efforts to call for an ambulance. I kept telling him nothing was wrong with me, I didn't even hit my head on anything.

Long/short: Three days later, I'm in the emergency room being diagnosed with a concussion. Seems that a hard jolt can cause the brain to impact the inside of your skull.

Do I wear a helmet? Yes, sometimes.
Do I believe it will protect me from a concussion or a black out after a minor crash? No, I've already have been given proof that an external impact is not required.
Do I believe, like my co-workers seem to think, that a helmet will save my life if I'm hit by a car? No. Everyone I know that has been hit (or killed) by a car, were wearing helmets and suffered internal injuries, broken bones, or cuts. None suffered from head injuries from an car/bike crash.