Because of the long lead time between ordering equipment and commissioning, power-system planning has always catered explicitly for uncertainties. In the past, elaborate deterministic techniques have been used, but there are now doubts about whether the out-turn from such sophistication justifies the efforts required. Perhaps a more flexible, informal approach to both planning and uncertainty is the answer, e.g. to be able to alter course to take account of actual conditions; also, optimisation techniques might be changed. Unexpected power-system structures, reliability and loss levels, and also generation plant mixes, might well result, which are better for meeting actual requirements than those at present