What is Non-Linearity?

Non-linearity means that a change in a system's input does not produce a proportional change in its output. Small actions can trigger disproportionately large effects, and large efforts can sometimes produce almost no visible change, which breaks the common intuition that outcomes should scale evenly with effort.

Recognizing non-linearity keeps systems thinkers from assuming that doubling an investment will double a result, or that a policy that failed at small scale is proven wrong, since thresholds, tipping points, and delays in complex systems routinely produce responses that look nothing like a straight line.