[sofixa]

Once in a bad situation is enough for permanent brain damage. Another bike or a car making a sudden move, someone hitting you, etc. Curbs and cars provide for dangerous landing spots if you fall.

I know of two separate people who were biking as a part of their daily commute without a helmet, and woke up in the hospital with zero recollection of what happened, but multiple issues (such as one of them being unable to concentrate or remember things).

[machinawhite]

So did the two seperate people fall, or get hit by a car? I know zero people who hurt themselves badly on a bike, but I know two that got hit by a car as pedestrians, so going with my anecdata walking is much more dangerous than biking

[sofixa]

That's the "fun" thing about it, neither of them actually know. They woke up in the hospital and have no recollection of what happened.