But links never exist in isolation. They always comprise a circle of causality, a feedback “loop,” in which every element is both “cause” and “effect”—influenced by some, and influencing others, so that every one of its effects, sooner or later, comes back to roost.

The practice of systems thinking starts with understanding a simple concept called “feedback” that shows how actions can reinforce or counteract (balance) each other. It builds to learning to recognize types of “structures” that recur again and again: