Scenario development and practical decision making under uncertainty

In this paper, we address the question of how flesh-and-blood decision-make rs manage the combinatorial explosion in scenario development for decision making under uncertainty. The first assumption is that the decision-makers try to undertake 'robust' actions. For the decision-maker, a robust action is an action that results in sufficiently good result whatever the events a re. We examine the psychological as well as the theoretical problems raised by the notion of robustness. Finally, we address the false feeling of deci sion-makers who talk of 'risk control'. We argue that risk control results from the thinking that one can postpone action after nature moves. This 'ac tion postponement' amounts to change look-ahead reasoning into diagnosis. ( C) 2001 Elsevier Science B.V. All rights reserved.