“Artificial, man-made mechanical and engineering contraptions with simple responses are complicated, but not “complex,” as they don’t have interdependencies.”
“But with complex systems, interdependencies are severe. You need to think in terms of ecology: if you remove a specific animal you disrupt a food chain: its predators will starve and its prey will grow unchecked, causing complications and series of cascading side effects”
“In the complex world, the notion of “cause” itself is suspect; it is either nearly impossible to detect or not really defined.”

— Excerpt From: Nassim Nicholas Taleb. “Antifragile.”