Play can only exist in the space between understanding and mastery.

Understanding is the moment when a player can effectively use their skills in the game.

Mastery is the moment when a player’s skills are so developed that there is no further discovery, only execution.

A game should endeavor to have a skill floor (understanding) as low as possible, and a skill ceiling (mastery) as high as possible, in order to maximize the period of enjoyment players can derive from it.

But beyond having this wide space, a game must also offer skill progression. A player must understand how their moves led to their outcomes, and how those outcomes could be improved by different moves next time.

Achieving skill progression requires the game to have clear causal links between moves and outcomes.