Gestalt Principles are defined as principles/laws of human perception that describe how humans group similar elements, recognize patterns and simplify complex images when we perceive objects. Google also defines gestalt as an organized whole that is perceived as more than the sum of its parts.
When relating this to game design, I think Difficulty could be considered a Principle of Gestalt that is specific to games because most graphic design elements are not interactive in the long run if at all. Designing with difficulty in mind plays into a lot of important systemic choices and can be a determinant of accessibility, flow, and tiempo. Difficulty is important to a game because if there is not balance (ex. something is too hard or too easy) the user may not want to engage with your game any further due to frustration or boredom. Difficulty, although commonly associated to Combat, is not exclusive to Combat but can rather be related to a myriad of other systems. For example, Crafting, Puzzle, Movement, and Random Generation can all be affected by the intended difficulty design. I would also argue that difficulty can apply not only to the systems the player interacts with overtly but covertly as well for example UI intuitiveness.
Difficulty Application Example - MC
Many games offer the choice of selecting your own difficulty. This allows for developers to consider several difference skill levels and adjust each system accordingly. Specifically with Hardcore mode in Minecraft the life and health system is completely altered, in combat enemies do more damage, the hunger system is altered, even Random mob generation is altered (more likely to spawn if armor and weapons). In juxtaposition, on peaceful mode, these systems are altered to favor the player (ex. you can't die to hunger, mobs do less damage, etc)
Difficulty ??? Example - Dark Souls
I struggled with deciding where to place Dark Souls because of the fact that it is incredibly difficult but does not allow the player to choose their own difficulty (An Interesting Read). I think a valid argument could be made either way that states Dark Souls does or does not consider difficulty, however I think it does because it is consistent throughout its gameplay. Dark Souls is impossible from start to finish, and the developers made those conscientious choices to make the game with this goal in mind.
Difficulty "Failures" Example - Any unbalanced game or mechanic
I would say most developers aim to balance their difficulty and design around any potential threats to balanced gameplay however sometimes their are unintentional slips in any game one could argue. For example, several people agreed the GTA cops were quite difficult to outrun and others claimed the difficulty balancing in Destiny quickly made certain weapons, armor, and boss/enemy interactions, meaningless as soon as the next update was released. I also found interesting that many developers now balance their game to favoring the players based on the "hard" mode present in the game. This can be seen in God of War, where the developers had playtested their own game for so long that they had to make it easier for those less accustomed to the controls.