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?