Page "Persistent world" Paragraph 4

Persistent worlds can be simulated in offline games, such as in the Animal Crossing series.

Even though nothing happens while the game is off ( due to the obvious technical constraint ), the illusion of persistence is created by advancing events as soon as the game is turned on.

The game generates events that could have happened during the real-world time in which the game was inactive.

NPC development is also seen as a key factor in maintaining offline and online persistence.

A method for creating NPCs that evolve and adapt to gameplay is seen in research done on motivated reinforcement learning agents.

Further persistence is possible if NPC interact with players in an adaptive way rather than a static method without regard to prior experiences.