The Principles of Game Design, #4
Every piece of a game’s method must reflect the game’s object, unless that contrast is part of the game’s object.
A game’s method is defined as the manner in which a game conducts itself — the rules, actions, and objects that comprise play, and the way that they interact. A game’s object is the overall idea that the game serves to communicate. Whether or not the designer has considered the game’s message, by the act of playing the player will receive one.
Every action is a verb, and every object is a noun. The game tells a story by the manner in which every action happens to every object. Therefore everything that you ask the player to do, however minor, is a part of the message that you are communicating to the player. Taken as a whole, the most common behaviors over the course of play define the perspective that the game communicates to the player.