All games use mechanics; however, there are different theories as to their ultimate importance to the game. In general, the process and study of game design are efforts to come up with game mechanics that allow for people playing a game to have an engaging, but not necessarily fun, experience. The interaction of various game mechanics in a game determines the complexity and level of player interaction in the game, and in conjunction with the game's environment and resources determine game balance. Some forms of game mechanics have been used in games for centuries, while others are relatively new, having been invented within the past decade.