At the most fundamentally abstract level, games as rules constructs are essentially a collection of verbs and goals. In designing multiplayer experiences, it is critically important to clearly model and communicate how a player ought to relate to other players if they are to feel engaged with your world. The most effective way is to assign different or goals which intrinsically incentivize either cooperation or competition with one another. This specific Design Pattern is called a “Role”, and is the mechanical foundation of all Role Playing Games (though it is not exclusive to them).