It’s easy to agree that beauty is desirable, though what each person considers to be beautiful can be very different. Kim Jong Un and President Trump have signed an agreement in Singapore declaring that they will bring peace and security between their nations, more particularly that they are committed to denuclearization of the Korean Peninsula.

As with an imaginary agreement that beauty is desirable, it is just as easy to agree that denuclearization is devoutly to be desired. Whether this most welcome de-escalation of terror can be put into practice is the vital question. Whether the stoking of nuclear fire in North Korea lasts depends on the U.S. and North Korea reaching an agreement acceptable to each country. President Trump has defined this as a “complete, verifiable and irreversible accord that North Korea give up its key armaments.” But we do not know that this definition is in the signed accord or what North Korea means by denuclearization.

It is important that the two leaders have come together and stated in writing their commitment to make peace, denuclearize the peninsula and end the state of war between the two Koreas. This is a milestone for which the world gives thanks. However, the arduous and complex work lies ahead. There is good reason to reflect now on whether the two leaders will have the fortitude to reach their declared destination.

Both Kim Jong Un and President Trump raised expectations high for success in their meeting. The North Korean leader promised to keep his people safe from attacks. The implication: “We will not discard the fire and rockets we sacrificed so much to build over the reign of my grandfather and father. I will keep you safe.”

President Trump and his staff said that the U.S. will agree to the new treaty only if the rockets and atomic bombs are all destroyed and cannot be rebuilt. How will both leaders climb down from their positions of perfection to a middle ground that both can accept as good enough and the best we can get?

Such tedious and intricate negotiations will take years and require both a persistence and patience that the U.S. president has not so far demonstrated.

Kim Jong Un has acted in a consistent, though often reprehensible, fashion during his six years in office. He consolidated his power and demonstrated the nuclear power of North Korea that the world would respect. When he had accomplished this, then and only then, did he offer to negotiate.

This is the first time the U.S. has entered into a “top-down” major negotiation where the two countries agree first and then get down to the business of the particulars to make it work. The patience of Job is required on both sides as progression and regression dance together. President Trump has shown neither evidence that he can carry out detailed reasoning on a topic nor that he can stick with a topic for an extended period of time.

The major reason to believe that the two leaders may turn words into world-changing actions is that North Korea has now achieved its three-generations-sought goal, nuclear defense. Kim demonstrated to the world that he can go nuclear toe-to-toe with the U.S. He must now square the circle for his people with denuclearization plus national sovereignty and security. Trump seized this opportunity, but he certainly did not create the opportunity.

Now the hard work begins. Kim Jong Un has decided to negotiate now because he has developed formidable attack dogs – nuclear weapons and rockets. That he might find ways to cage the dogs is believable since he would achieve international status, ensure his tenure in power and bring a better life to his people. For this he might be willing to cage his attack dogs. But be assured he will not dispose of his attack dogs.

Roy Wehrle of Springfield is professor emeritus at University of Illinois Springfield and formerly Economic Counsellor, U.S. Department of State.