Contrary to popular opinion, among people who study systems theory, “complicated” and “complex” are distinct words with precise meanings. The engine inside a car is complicated. A complicated system is a causal system—meaning it is subject to cause and effect. Although it may have many parts, they will interact with one another in highly predictable ways. Problems with complicated systems have solutions. This means that, within reason, a complicated system can be fixed with a high degree of confidence. It can be controlled. This is not to say that a complicated system can’t be confusing or inaccessible to the layperson. Quite the contrary. Understanding a complicated system, such as an engine or a 3-D printer, requires specialized expertise and experience. Here, experts can detect patterns and provide solutions based on established good practice. This is the domain of the mechanic, the watchmaker, the air traffic controller, the architect, and the engineer. Traffic, on the other hand, is complex. A complex system is not causal, it’s dispositional. We can make informed guesses about what it is likely to do (its disposition), but we can’t be sure. We can make predictions about the weather, but we cannot control it. Unlike complicated problems, complex problems cannot be solved, only managed. They cannot be controlled, only nudged. This is the domain of the butterfly effect, where a small change can lead to something big, and a big change might barely make a dent. Here expertise can be a disadvantage if it becomes dogma or blinds us to the inherent uncertainty present in our situation.
Aaron Dignan in Brave New Work