Captain Anorak's Guide to Gaming
Captain Anorak's Fourth Rule for Game Mechanics:
It should not be necessary to understand the rules to roleplay a character

When a player chooses what his character does, he should choose an action done by a person in a world, not a use of rules done by a collection of stats on paper. Ideally, I should be able to choose my character's actions without understanding how the rules will deal with them.

There are two very broad approaches to writing games: there are story games, and gamepiece games.

A story game allows a story to unfold about what is happening to characters in the game, with the players making the decisions that those characters would make, and the game system resolving the outcomes of those decisions. The roleplaying game is the ultimate development of the story game: characters can make any decision they want - there is infinite choice. The game has an illusion of reality: I imagine that I am in my character's position and say, for example, 'I'm going to open the door and look cautiously inside.'

Chess is a gamepiece game. There is no story. The pieces in play are simply abstract gamepieces which represent nothing else. There is a completely limiting set of rules: pieces only move according to fixed rules, and can never do anything else. The aim of play is to use the rules to your own advantage to out-think your opponent. There is no concept of a reality in which these pieces are individuals: I would always say 'I'm moving my bishop' rather than imagining that my bishop is a person making a choice for himself based on what he can see and his own motivations.

In many roleplaying games, there is a problem: it is necessary for the players to know the rules for the game to be playable. For instance, in the D20 system, characters have special abilities called 'feats'. When a player wants to use such an ability he declares that he's using it. Players then have to know under what circumstances a feat can be used, which can be the cause of rules lawyering arguments. People also use tactics based on the rules: I might choose not to use a certain feat if I suspect that an enemy has a feat which would negate it.

This is bad because it moves the game away from being a story game into being a gamepiece game. Characters cease to be people who make the kind of decisions that people make in reality, and become gamepieces which are manipulated from the outside by a player who is making the best use of the rules he knows.