In a traditional role-playing game, most of the participants will be playing the associative game, so we will take a look at that first. The reason that most participants will be playing the associative game is threefold: (1) any given GM can run a game for a number of players, and in most cases, the game is more fun if there are at least 3 participants in the associated game, allowing the players to react to each other as well as to the game milieu, (2) it is the easier of the two games to play, in that it requires both less prep and a less skill varied to do well, and (3) for many people, it is where the majority of the fun and interest of role-playing games is to be found.
In its purest form, the players of such a game would not need to know or understand any rules at all. Who and what their characters were could be conveyed descriptively, and the players could make choices from that standpoint without knowing the rules that underlay their outcome. Of course, most players prefer to have some understanding of the basics of the game. The traditional rpg splits rules between those that the players should know, and those that the GM must know. In the early days of the hobby, it was very much discouraged for players to examine the GM rules, not because it removed the authority of the GM, but because it deprived the player of the opportunity to learn how the game milieu works from actual play; i.e., from an associated stance.
How to strengthen the associated stance has been a question that many groups, and many game designers, have tried to answer over the years. In some groups, for instance, the large-scale creation of the game milieu is devised by the players and GM as a unit - in other words, everyone participates in the dissociated game - so that the players will have the basic knowledge of the world that their characters would presumably have. Other games stress a world in which knowledge is scarce and precious. Still other games, like the classic Traveller and Hârn setting, produce materials that are designed to convey background information to players and GM alike.
Although some games have moved far afield in layering dissociated mechanics on the player's side of the table - 4th Edition D&D being an obvious example - much of the fun and interest in playing a traditional rpg comes from discovering the unknown within a game milieu where the player is able to act from his or her PC's point of view. If this is what you are interested in as a player, excessive dissociated mechanics are undesirable. Likewise, excessive input into the game milieu's composition is undesirable. Gamers love to tell stories about those moments in which the game turned 180° from what they expected, when they came to a sudden understanding of the connections that created a rational whole from what had seemed to disparate parts, when they miscalculated, when they came up with a solution to solve what had appeared unsolvable.
It is easy to find a player who will talk animatedly about when he resolved a mystery, or encountered the unexpected. It is very difficult to find a player who will be so enthused about when thing occurred exactly as expected.
This is the primary tension one sees in rpgs - The players want to win. They want to manage risk so that they increase the odds of their winning. Ultimately, the players strive to play it safe, BUT "playing it safe" only retains its interest so long as there is no way to play it completely safe. Managing risk is only fun when not all risk is manageable. A flat track does not a roller coaster make.