You have to take into account the odds when you look at severity.
There is a possibility that some quantum event will port me into another dimension where I will need a M4 and a plan to start a new civilization. If I didn't have such plans then the outcomes are severe. But this is unlikely and thus I leave my plans for a new civilization at home. When you say you plan for severity - that is because your realize that there is a small likelihood of the event but if that occurs it will be severe. But you don't plan for events that don't have that small but severe package.
When someone says they don't take into account the odds, that's just not true. We predict possible outcomes on most things we do.
Again, rational decision making takes into account the odds and the outcomes.