I was shocked to hear of the accidental death of Natasha Richardson. Then I remembered two books and one real-life incident that warned me such outcomes from what seems like a minor head injury are possible.
One book was a Lord Peter Wimsey mystery by Dorothy Sayers in which a medical case was cited of a young man who fell from his horse, seemed perfectly fine, assured his friends he was quite all right, then shortly thereafter died from his head injury. Unfortunately, I don't remember which particular book it was and don't have the time to look today.
Another was ROSE IN BLOOM by Louisa May Alcott, the sequel to EIGHT COUSINS. In ROSE IN BLOOM, Rose is being courted by the handsome, charming Charlie. Charlie, too, falls from his horse. He's capable of talking and doesn't feel very sick, but nothing can be done to prevent his death from his head injury.
I might have thought such deaths don't happen in this day and age, except for a real-life incident a few years ago that involved some young men trying to steal a car from an underground garage. The husband of an acquaintance saw them, intervened and was shoved backward. He hit his head on a concrete pillar and died as a result.
When I heard about Natasha Richardson and saw a picture of the beginner slope, I thought, "I probably wouldn't have worn a helmet, either." Scary thought, and if there's any good that can come from something like this, it's that many more people will wear helmets now, even on the beginner hills.