One of the biggest problems when playing any pen and paper roleplaying game is the disconnect between the image that resides in the GM's head and the image that lodges in the players'. This is the essential burden of communication that plagues human beings and has plagued them for as long as there has been language. Was Winston actually shot at the end of 1984, or was that a metaphor? What are we to think? Ambiguity in language and depiction is actually one of the cornerstones of good artwork. In a pen and paper roleplaying game, it strikes at the very foundation of playability.
It is impossible to play a pen and paper game and continually create ambiguous or uncertain images in the players' minds. They rely on the word of the GM to form a solid conception of the world. The "world" exists, canonically, only within the GM's own head. This leads to several corollary truths.
1) The world is usable only insofar as it is communicated.
2) Players misconceptions can only be rectified by reference to the GM's knowledge.
3) All disputes as to ambiguity must be resolved in the favor of the GM.
3a) Creation of ambiguity is a failure on the part of the GM.
4) Open lines of communication are critical.
1. The world is usable only insofar as it is communicated. Players cannot make use of uncommunicated details. They cannot rely on details that reside in the GM's head alone. However, since the GM is in charge of relaying that information to the players, there should never be intentionally uncommunicated details that the player-characters would otherwise have access to. This strikes at the foundation of the playability of the game.
2. Players misconceptions can only be rectified by reference to the GM's knowledge. Because the setting is contained within the GM's mind, mistakes and misconceptions can only be solved by recourse to the GM. Players cannot rectify their misconceptions by thinking about them; they cannot rectify them by thinking about them or asking each other. The GM is the only person who has the knowledge required to straighten out misconceptions.
3. All disputes as to ambiguity must be resolved in the favor of the GM. This extends the previous fact: if the players cannot resolve the misconceptions or ambiguities on their own because the GM holds the entire setting in his mind, then all ambiguities must be resolved in the favor of the GM. The setting is contained by the GM's mind, encompassed by the GM. It only exists as a complete concept within the GM's thoughts--communicating those thoughts to the players is the GM's biggest challenge.
3a. Creation of ambiguity is a failure on the part of the GM. Just because ambiguities must be resolved in the GM's favor, that doesn't mean this is a good thing, to be embraced. The creation of ambiguous situations that must be interpreted are failures on the part of the GM. The GM should struggle to keep ambiguity out of the game when it comes to the position of enemies during fights, understanding the expressions on NPC's faces, the layout of rooms, and every other niggling little detail. Yes, those details must be resolved in the GM's favor... but if you encounter a time when the GM has failed to express them properly it is always the GM's fault.
4. Thus, open lines of communication are critical. Because it is difficult for a GM to know whether or not his words have been understood, it behooves players to be more cautious than not when interpreting them. Questions are important. "Let me see if I understand this... the orcs are here, arrayed this way. What are they armed with, again?" Questions like these on the player's part help the GM (and the players) ensure that they're on the same page.