To compel the other side to negotiate, you need pressure and leverage, it is assumed. For the other side to agree to change its behavior, however, you need to offer giving up that leverage as an incentive. But once the pressure is relieved, so is the incentive of the other side to comply with the agreement, the paradigm dictates, causing the deal to fall apart.
The paradox is caused by a flaw in the paradigm's foundational assumption: The behavior of the other side can only be changed through pressure.
There is no solution to this paradox. The paradigm needs to be discarded altogether.
Rather, any deal needs to be embedded in a web of other arrangements that changes the incentive structure of both sides. The leap of faith both sides must take to strike a deal must be balanced by measures following the deal that tie the two together and raise the cost for reverting back to the previous posture and policies.
For Iran, the prospect of shedding its pariah status and being integrated into the political and economic structures of the region and the global economy will be a profoundly potent deterrent against any impulse to restart the controversial dimensions of the nuclear program. The fear of losing this new acceptance will be more powerful than the fear of shouldering new economics sanctions.
For the U.S., the reduction of tensions following a nuclear deal and increase in discreet collaboration on regional matters such as the efforts against ISIS in Iraq, will be of tremendous value. As Ali Shamkhani, Secretary of Iran's Supreme National Security Council said last month: After a nuclear accord has been signed, Iran in the United States “can behave in a way that they do not use their energy against each other." The cost of losing Iran as a neutral, or better yet, stabilizing force in the region will be a stronger deterrent against any foul play on sanctions relief than Iran retaining a few more hundred centrifuges.