Hartford Fire Insurance Co. v. California is like when you play a game with your friends and you all have different ideas about what the rules are. In this case, Hartford Fire Insurance Co. is a company that provides insurance for things like buildings and homes. California is a state in America that has its own rules about how much insurance companies can charge people.
The problem was that Hartford Fire Insurance Co. wanted to charge a lot of money for their insurance in California, but the state said they couldn't. So the company went to court to try to get the state's rules changed.
The judges in the courtrooms had to decide who was right - the insurance company or the state. They looked at the rules in California and compared them to other states to see if they were fair. They also looked at what the insurance company was trying to do and whether it would be good for the people of California.
In the end, the judges decided that the state's rules were fair and that the insurance company couldn't charge as much as they wanted. This was because the rules were there to protect people from paying too much money for their insurance.
It's like when you play a game with your friends and you all agree on the rules before you start. If someone tries to change the rules halfway through, it's not fair and everyone will get mad. So the judges in this case made sure that the rules stayed the same for everyone in California.