Complex systems are characterized by the fact that they consist of components that interact with each other, have feedback effects and non-linear, unpredictable behavior.
"As humans, we are used to thinking in linear cause-and-effect relationships: the harder a ball is kicked, the farther it flies, the further a pendulum is deflected, the greater the amplitude, etc. Cause and effect can be clearly distinguished, which is why problems are solved by fighting the causes. All this no longer applies to complex systems. In complex systems it is often not possible to determine exactly one single cause for a certain behaviour of the system. In addition, the system behaviour is often extremely sensitive to the initial conditions and cannot be predicted exactly after a short time; small causes can have huge effects ("butterfly effect"). Sometimes unexpected reactions occur, sometimes the achieved state is even the opposite of what was intended.
As the complexity researcher Stuart Kauffman has shown through numerical simulations, even very simple mathematical, so-called Boolean networks - these are networks in which the nodes are only possible in two possible states and the connections are only possible as AND and OR - already show chaotic behaviour at a very small number of connections of four to five nodes. So, if in such a network every node is connected to 5 others, the result is chaotic behaviour - predictions are no longer possible. But the number of connections of 5 per node is not very much."
Source: The book "Ist Nachhaltigkeit utopisch?", page 74 by Prof. Dr. Christian Berg, published by the publishing house oekom in the year 2020