So why do RPGs have rules?
Because of the central mechanic that defines an RPG where
- The referee describes a setting
- The players describe some character they want to play in the setting.
- The referee describes the circumstances in which the characters find themselves.
- The players describe what they do as their characters.
- The referee adjudicates what the players do as their characters and then loops back to #3.
Steps 3 and 5 repeats until the session or campaign ends.
If the referee is a good teacher, coach, and communicator. Knows the setting of the campaign very well including what is possible for characters to do. An RPG campaign can be played without any reference to a system. However, the skill required to make it fun and doable as a hobby is high enough that most folks turn to a written system.
Having an RPG system saves the players and referee time and work in several ways.
- As a terse form of communication as to how a setting or genre works.
- The system mechanics will provide a terse and often precise description of various elements of the setting like characters, and objects.
- By teaching the referee and players how to handle common situations that arise in the setting or genre. Determining when there is a certain success, a certain failure, or the odds are uncertain, thus needs to be resolved with a procedure.
- As a reference so that similar rulings are made for similar situations.
This allows the group to spend more of their limited hobby time and verbal bandwidth on playing the campaign. Rules are not a requirement to run an RPG campaign but having a set of rules make it more fun and doable in the time one has for a hobby.
The key element for tabletop roleplaying that elevates it above "Let's Pretend" that makes it work is the judgment of the human referee, not the rules. The rules are an aide and a tool to make this happen easier as a fun pastime.
Where it gets messy is in the implementation of the system. The only firm requirement that the system needs to follow is that the mechanics reflect the setting of the campaign accurately. If they don't then either one of two things will happen. The rules will be modified to reflect what missing or the setting will be altered to reflect how the rules describe things.
Beyond that, it is a purely personal preference. Are characters described using class and level or skills and talents? Is armor about avoidance or damage resistance? Does social interaction get the most detail, is it combat encounters? Or both. Level of detail and focus are often the main drivers in which set of rules the group finds fun and interesting.
As long as the result is consistent with the setting and the group finds it fun to play there is no right answer. The loose analogy I like to use is that it doesn't matter whether the car is painted red or blue., they both will get you to your destination. But you may have more fun getting there driving a red car.
Again while this is easy to describe, the implementation is messy given the flexibility of the core mechanic that all RPGs share.
