To lose yourself in the fantasy of the game is to become immersed in it. Immersion occurs whenever the game becomes so utterly engaging that your perception of reality subsides and is replaced by the virtuality of the game world. A primary goal of any good designer is to plunge the player so deeply into the game that they forget the outside world for a while. Your job is to craft the world, story, mechanics, and characters in such a way that the player suspends their disbelief, accepts the premise of the game, and then immerses themselves entirely into it. If the material is engaging the player will overlook any minor inconsistencies and enjoy the game.