the man who lives next door to you often rides his bicycle in the company of his two young children but without a helmet. in fact, on several occasions, you have seen him riding with his helmet hanging by its straps from the handlebars. his young children sometimes wear a helmet, sometimes not. if the man fell off his bicycle and hurt his head in a way that would have been prevented if he had worn a helmet, would it be reasonable to ask him to contribute towards the treatment costs for his injury?