“We are all about quantifiables: how many centrifuges can spin, how much plutonium can come out of the Arak reactor, how much uranium you can have on hand,” one senior American official at the center of the negotiations said the other day on the condition of anonymity because of the secrecy the United States is trying to enforce around the talks.

“They are all about symbolism, about avoiding the optics of backing down,” the official said, even if it means engaging in expensive, inefficient nuclear enrichment activity that makes little economic or strategic sense.

There is a sense that the hurdles would be lower if the negotiations were limited to Mr. Kerry, Energy Secretary Ernest J. Moniz and their Iranian counterparts. By all accounts, their working relationship is strong; Mr. Kerry has now spent more time with Iran’s jovial, American-educated foreign minister, Mohammad Javad Zarif, than with any other foreign minister.

Mr. Moniz talks enrichment and reactor technology with the head of Iran’s atomic energy agency, Ali Akbar Salehi; while they have disagreements, they are almost all about technology, not ideology. Both Iranians were trained in the United States before the 1979 revolution, and while they cannot say so, both clearly appear to see this nuclear negotiation as a way to end the days of Iran’s defining itself by its opposition to the United States.