A game is a complex system that derives its distinct features, like challenge and surprise, from emergence.

Games capture the player because they are full of surprises ! We do X in the game and something 'unexpected' happens. It would be very difficult, even impossible, to predict this behavior in advance even if we would know all the elements in the game. This is called emergence {1 + 1 > 2}. Since Aristotle, emergence is the distinguishing feature of complexity. Take the example of SimCity - it is impossible for two players to create exactly the same city, even if the players take the same decisions. The smallest difference in the decisions of the two players - one being a fraction of a second later, a millimeter further to the right - may be the cause of a completely different city after hours of game-play. This is the Butterfly effect (Chaos theory) one of the branches of complex systems. Understanding and managing complexity is key to all grand challenges in modern society - climate change, migration, international relations, financial stability, virus control, terrorism, cyber security and so on. They are full of emergent behavior, which makes them difficult to understand, let alone to communicate about them and find the effective strategies to manage them. Because games themselves are complex systems, the aforementioned grand challenges can be modeled, explored as games, and management strategies can be tested within the game environment.