The tactical situation is dire and the course of action clear—pull back your forces to defensible terrain, shortening your supply lines and providing mutual support for your thinly-stretched units. But you can’t, because there’s an idiot rule in your way.
Wargames use idiot rules to prevent players from taking actions that are otherwise tactically sound and allowed in the rules, justifying the restrictions for historical reasons or to provide some form of play balance. After all, unless forced by the rules, very few sane gamers would throw division after division into Stalingrad or try to hold all of France in the face of a massive Allied invasion. Idiot rules attempt to enforce dictates from above the gamer’s pay grade.
Idiot rules can be subtle, offering rewards for following a particular course of action; games that use Victory Points as a means of determining the outcome of a game, for instance, can allocate a certain number of VP for control of locations that would otherwise be abandoned posthaste. Idiot rules can also be explicit, making certain sections of the map simply off-limits until a certain game turn or until certain criteria have been met.