All systems are not equal. There is an important distinction to make when describing systems. This may seem semantic or academic but understanding the difference will change how you approach making system changes.
Complicated systems have predictable outcomes. They follow rules even though they have many moving parts. Complicated systems won't change over time. Complicated systems are deterministic. Example: an automobile engine
Complex systems behave unpredictably. There are interactions between the internal components that produce different results given the same input. Complex system can change over time with no outside stimulus. Complex systems are non-deterministic. Example: Natural systems
MIT Sloan Review article