Wicked problems were first defined by Horst Rittel and Melvin Webber in 1973. Horst and Webber introduced the term to differentiate between tame or linear problems that have single solutions and highly complex problems that have no right or wrong solution. In their article “Dilemmas in a General Theory of Planning” they specified ten characteristics of wicked problems in a context of social policy planning:

1. There is no definitive formulation of a wicked problem.
2. Wicked problems have no stopping rule.
3. Solutions to wicked problems are not true-or-false, but better or worse.
4. There is no immediate and no ultimate test of a solution to a wicked problem.
5. Every solution to a wicked problem is a “one-shot operation”; because there is no opportunity to learn by trial-and-error, every attempt counts significantly.
6. Wicked problems do not have an enumerable (or an exhaustively describable) set of potential solutions, nor is there a well-described set of permissible operations that may be incorporated into the plan.
7. Every wicked problem is essentially unique.
8. Every wicked problem can be considered to be a symptom of another problem.
9. The existence of a discrepancy representing a wicked problem can be explained in numerous ways. The choice of explanation determines the nature of the problem’s resolution.
10. The planner has no right to be wrong (planners are liable for the consequences of the actions they generate).

Rittel, Horst, and Melvin Webber; Dilemmas in a General Theory of Planning, Policy Sciences, Vol. 4, pp. 155-169, Elsevier Scientific Publishing Company, Inc., Amsterdam, 1973.