GameSetWatch is running a piece discussing some of the ways in which gameplay can progress from simple to complex. The author talks about how acquiring items, new abilities, or just increasing the player's overall effectiveness can make it difficult for game designers to keep their content balanced and interesting. Quoting: "What do I mean by progression? There are at least two distinct types of progression in computer games, which I'll label player progression, and character progression (narrative progression is arguably a third). Player progression is the increasing aptitude of the player in mastering the game: whether through learning and understanding the technical rules of the game (surface play) or the implications of those rules (deep play). ... Character progression is the unlocking of additional rules of play, or altering the existing rules, by choices or actions within the game."