In the future, for the two sides to reach a comprehensive nuclear deal, they still have to address two major challenges. And the first one is their long-existing trust deficit.

In fact, the nuclear problem is indeed a product of decades of distrust between Iran and the US-led Western hemisphere. In order to maintain the West's control of Iran's oil resources, the United States, with the help of the British, staged a coup and restored in the country the rule of Mohammad Reza Shah Pahlavi in 1953.

However, the Shah of Iran was toppled in the 1979 Islamic Revolution, and that was exactly when Tehran and Washington began to turn against each other as adversaries, while their relations constantly deteriorated in the years afterwards.

Therefore, it is almost impossible for a pair of foes to cast away their old animosity, regain the lost trust and repair the damaged relationships in a period of time as short as several months.

In fact, the coming months could be even more perilous. Once the negotiators still cannot produce enough substantial advancement at the ensuing talks, the hard-liners back in Iran, the United States and Israel would be emboldened while the talk of distrust would ramp up again, leaving those willing to talk little room to compromise.

Additionally, another major challenge the negotiators have to cope with is how to bridge their remaining significant differences over sanction relief and uranium enrichment.