Everything has rules. Life works because of rules. Rules have many names and forms. Laws of physics, algebra, logic, frameworks, instructions and more. Without rules you have chaos. That said, some scientists think even chaos has rules.
In games, rules are vital. However free and open a game may seem, there will be a deep set rules that cannot be broken. Be it the size of the map or the way physics work in the game. Minecraft is a good example. Seemingly you can do anything. However, you have to follow rules and instructions to gain that freedom. You have to mine and craft and create – all within the rules of the world around you.