Often, one of the challenges in understanding a system is knowing what to consider “inside” and “outside” it. By this I mean which elements are part of the system — affecting its outcomes — and which aren’t.
Consider a common system most of us have experience with: an automobile. An auto is made up of parts and subsystems (chassis, wheels, engine, transmission, etc.) that relate to each other in various ways to allow it to serve its purpose. (Transport us from one place to another.) Everybody knows what a car looks like. If you ask a child to draw a one, she’ll probably make a picture like this one:
The drawing features some of the parts of the car system we experience when we interact with it, and which set it apart from other things we experience in the world: the passenger cabin, the wheels, the steering wheel. This drawing – which I posit as representative of the mental model most of us have of cars as a system — shows a free-standing object in the world. However, a car with an internal combustion engine will not go very far without fuel. Fuel and the means of getting fuel into the car are essential parts of the car-as-system.
So is the fueling station — and the network of such fueling stations it belongs to — part of the automobile system, or not? From one perspective, it is; the car can’t achieve its purpose without it. The car and the fueling network make up a bigger system of which the car on its own is but a mere subsystem. We can examine this subsystem independently, but at some point we must consider the broader system if we are to understand how it accomplishes its purpose.
But from another perspective, it’s helpful not to have to think about the fueling network. For example, if we’re tasked with designing a new car, we should not also expect to have to design the system that provides fuel for it. The network of fueling stations is an incredibly complex system on its own. Fortunately, standard interfaces exist that allow the car system to tap into the fueling network system. Car designers only need to concern themselves with accommodating this interface. (Obviously, this requires that both systems be reasonably mature. The incoherence of current charging networks is one of the challenges facing electric car manufacturers.)
So what is considered to be inside and outside? As with so many other issues related to complex systems, the answer is “it depends.” People bring different perspectives and concerns to the systems they’re interacting with, and ultimately that’s how we define their boundaries.