Why is it important for judges to apply the law to cases based on facts and law and not just their own opinions?

Sara and her friends were at an iowa football game in iowa city. sara is a life long resident of iowa and goes to college at dmacc. while she was in iowa city, robert smashed into her car when he ran a red light. sara was seriously injured and taken to university hospitals in iowa city (fortunately her injuries were not life threatening but laid her up for a long time and she had to drop out of college for the rest of the semester). robert is from michigan and was in iowa city to see the game and then to party later. at the time of the accident robert was drunk (at least legally - he blew a 0.17 and the limit is 0.08). sara has sustained about $500,000 in damages between her current and future medical bills, pain/suffering, lost wages, etc. also her car was totaled in the accident. can sara sue robert in a federal court? explain why or why not. (be sure to mention the two primary factors associated with suing someone in a federal court in a case like this.)