Balancing can be tricky, if all players should be able to beat the game all choices should be viable ways to go, and nothing is obviously exploitative. The system in the world should also be able to run without breaking the play experience. I found an example from the development of The Elder Scrolls 4: Oblivion, where the developers had given the NPC’s their own goals and would kill each other and make the player unable to complete the game. This naturally did not end up in the final version.
One of the most important factors for creating a successful systemic world is that the systems and rules must be consistent, so the player can navigate the game world and plan their moves based on these systems. I.e. if wood can burn, all wood must be recognisable as wood and be able to burn, if metal attracts lightning all metals should attract lightning etc. The systemic worlds allow the designers to create a dynamic world that feels consistent and like it would run without the players input.