We often think of games in their totality as singular objects; however, as explored in Koster’s Taxonomy of Games, the definition of a “Game” at its core is “a unique rules construct”. The implication of this is that when you pick apart the core components of a game, it’s revealed that those individual mechanics themselves for smaller games. These individual games and their component mechanics can be further abstracted into Game Design Patterns that can be modified or interchanged.
Practical Creativity by Raph Koster, GDC 2014 Tips for Creative Game Design