A game is a complex system. It is a miniature world, in many ways analogous to the world we live in. The game occurs in a space or setting. It has its own physical laws or rules. It engages people or players, who generate outcomes by making choices and taking actions. Learning occurs largely by trial and error, and through this learning a clear goal or goals emerge. There is a sense of progress, a system of feedback, incentives, reward, punishment, reputation. The only difference is that the game world has been 100 percent designed, and it is an experience players can choose to walk away from. This means game designers must capture and retain players' attention and interest quickly.