A cybergame designer might create a game with one hundred different enemy types with which the player can fight. This is easy to do. The coder creates a single enemy type with multiple properties (such as name, strength, endurance, etc). Creating the 100 enemies then becomes a matter of instantiating 100 of this enemy and entering a variety of values for the properties. There are other ways, this is one.
However, these enemies would only exist for the player once they were placed in the game space. If the designer chose to hide them, or never actually placed them anywhere, they would, in an almost existential way, not exist. The complexity of the game environment would be reduced, despite all the potential complexity these enemies provide, because the designer has filtered them out or ignored them. The variety of the game can be attenuated through ignorance (some problems can be ignored until they go away).
This regulation of the game’s complexity then becomes a design strategy. It is a fairly common strategy, seen in games from Civilization V to The Lord of the Rings: The Two Towers. The player is first introduced to a few dangers or enemies, providing that player with the opportunity to learn the game system and experience the game world. As these players learn, they develop their own methods for managing the game world’s variety and the game design can provide more variety without over-whelming them Alternatively, increasing variety can be a powerful tool for overwhelming a player; perhaps after they have declared war on the wrong nation or wandered into the wrong part of Middle Earth, the game design releases so many warring bands or murderous orcs and monsters that they player can not provide the requisite variety to deal with them and is destroyed.