When people are playing a game, they need to follow the rules. If they don't, the game becomes disorganised and unfair, and it stops being fun. If a student ignores a rules against talking in class,the other student can't concentrate. Driver who don't follow traffic laws can cause serious accident.
Most things we do are governed by rules. These may be unwritten, like the rules of social politeness, or official laws passed by parliament and backed up by the legal system.