We all dealt with complex systems long before we learned logical and systemic analysis. We are complex systems; our bodies are wonderful examples of integrated, interconnected, and self-preserving complexity. Every person we meet, every organization, every animal, garden, tree, or forest is a complex system. We have formed a practical understanding of how these systems work and how to deal with them intuitively, without analysis, and often without words.

So, what is a system? A system is a collection of things, people, cells, molecules, or whatever, connected in such a way that they produce a specific behavioral pattern over time. A system may be stimulated, constrained, or guided by external forces, but the system's response to these forces is shaped in its own specific way, and this response is always complex in the real world.