Rather than a Folie à Deux, call it a Folie à 5+1: a mutually reinforcing delusion involving Iran, the United States, Russia, China and the Europeans. What makes the outcome of the Iran nuclear deal so dangerous is that none of the parties to the agreement has thought through the consequences of its actions, least of all Iran itself. They are not so much sleepwalkers, as historian Christopher Clark characterized the combatants who stumbled into World War I, as waking fantasists.
There is one state of the world in which things go right, namely, Iran’s passive acceptance of national decline. There are innumerable ways in which everything can go terribly wrong. Game theorists who try to construct a decision tree from these criteria would assign a very low probability to a good outcome and a very high probably to a bad one.
Iran believes that it will lead the Shi’ite Muslims of the region to restored power; America believes that Iran’s enhanced status will foster a beneficial balance of power; China believes that the balance of military power between the Sunni and Shi’ite states (and between Iran and Israel) will prevent war; Russia believes that Iran will serve as a counterweight to the Sunni jihadist that threaten its southern flank; and the Europeans as usual close their eyes and hope for the best.