Obsidian Entertainment - The Queen Needs No Advocate
The intriguing title The Queen Needs No Advocate is a piece on J.E. Sawyer's personal blog about high-level systemic design, using chess as an illustration:
Gameplay consists of players making (more-or-less) informed decisions about what they need to do to overcome an obstacle. It is not enough for the obstacle to be clearly defined and communicated to players. They also need to have a clear understanding of what tools are at their disposal to solve the problem. In chess, the player's primary tools are his or her pieces. Though circumstances determine the value of pieces on any given move, no one needs to advocate the fundamental value of the queen in chess.
As an extreme analogue in video games, it's unlikely that many players need to be told what the value of the HECU RPG is the first time they find one in Half-Life. After being pursued by a relentless Apache helicopter over numerous maps, the player winds up in a cave with the RPG on the ground and the Apache hovering outside. Players typically snatch up the RPG and blast the Apache in moments. Though the HECU is not the "queen" of Half-Life's weapons, it has obvious applicability in the circumstance where it appears.
When designers develop tools, we should strive for clarity of primary purpose in a player's tools. The more obvious we make the value of the tools at a player's disposal, the more quickly the player will spend time fully engaged with the obstacles at hand instead of trying to figure out what they aren't "getting".