Activision's James Portnow discusses the many different kinds of arcs in games, and how they can serve as a means of keeping a player invested in a game.
The arc is what makes us feel invested in a game. It's the hook that keeps us playing. Without that feeling of investment, we'd put down a game as soon as we tired of the action.
The arc is also what keeps the action fresh. It changes, or at least contextualizes, the action so that the player doesn't feel as though he or she is simply doing the same thing over and over again.
Read on for some of the types of arcs that are commonly found in games.