The medium of tabletop role-playing games is such that every single rule must go through a series of steps from declaring intent to do something, to the actual handling of the mechanical bits, to the resolution and reintegration of “what happens” in the fictional space. So for every rule that exists, the table must make a ruling over its use and effects.
I will try to avoid going into designer jargon land or reference dead theory [*], but the point I am trying to get across is that no matter how detailed or instructive a rule is in a game, the humans at the table still need to interpret the rule, acknowledge when and where it is going to be used, and decide amongst themselves how and what happens.
If a game tells you to roll a die when your character attacks, and if you get some number you do damage – who actually decides when this happens? What is a sufficient attack? Does the player get to direct where they attack or just their intent? Do they get any part in narrating the outcome? Does the result on the to-hit roll confer additional information, such as rolling extremely high might let the player put their opponent at an additional disadvantage?
Or take Apocalypse World’s Read a Sitch move – it says when examining a charged situation. What does “charged” mean? Who determines that? Can the player ad-hoc add context to make an otherwise un-charged situation charged? How much veto does the referee have?
Most games don’t actually explicitly answer many of the above questions. Of course the general assumption for traditional role-playing games is “the referee decides”, but how the referee and the table culture draws the line on these kinds of things varies quite heavily from table to table, and the exact differences may widely shift how the game is experienced between different play groups.
If two groups pick up OD&D and the first plays it like a very regimented wargame, the second more in a loosey goosey narrative fashion, neither are playing it “incorrectly.” Its also not an “accident” if someone interprets a rule differently from how another person tries to read the “design intent” of the game. The game doesn’t belong to the designer, it belongs to the players.
This is why role-playing games are so awesome. The game is yours. No designer and no judge has any right to come to your table to tell you that you’re doing it wrong. The methods you find to work for you, to portray and play your worlds are the right way. If you want to pick up new styles and techniques you converse with other gamers, you chat about things you tried, how that worked out, how people responded, and we as a culture refine our toolbox.
* edit: I am specifically talking about things like Big Model & IIEE, my pal Panic Pillow made a post examining this concept from a more philosophical stance, which is an excellent read