The fact that we will never know all of the specific risks is an argument against worst-case thinking. No matter how many contingencies you try to account for

The fact that we will never know all of the specific risks is an argument against worst-case thinking. No matter how many contingencies you try to account for in your baseline system, there will always be risks that you cannot account for, which will become the new worst case. So, by definition, you can never actually avoid the worst case. (Even if you may end up with a worst-case situation that isn't as damaging as the ones you've accounted for.) But the real solution is to distinguish risk avoidance against risk response. Prescriptive solutions tend to focus on avoiding risks, and building those avoidance methods into the baseline system that applies generally. But if we isolate the unlikely risks in the way that lotharbot suggests, we can draw a line across the likelihood axis and say "we'll avoid the risks on this side of line and deal with the outliers on a case-by-case basis." The best strategic slack is to have a robust way of handling unexpected occurrences after the fact, so you optimize the prescriptive system to the expected general case. BTW, I'd bet there's a pretty strong correlation between "risks that we can't account for" and "risks that are unlikely to occur".