It also remains far from certain that putting yet more time on the clock will help, when after 10 rounds of talks the two sides still remain poles apart on the fundamental issues.
US Secretary of State John Kerry admitted as much on Monday after he and foreign ministers from Iran and the other powers decided to extend their deadline for a deal to July 1, after intense days of talks in Vienna.
"These talks aren't going to suddenly get easier just because we extend them," Kerry told reporters. "They are tough. They have been tough and they are going to stay tough."
Kerry and his Iranian counterpart Mohammad Javad Zarif stressed that some progress has been made, with Zarif even suggesting that a deal was possible "much faster" than in seven months. They aim to have the outlines by March.
But it is clear that when it comes to the two main sticking points -- the future scale of Iran's nuclear programme and the pace of sanctions relief for Iran -- they remain perhaps as far away as ever.
The five permanent members of the UN Security Council plus Germany want Iran to dismantle large parts of its activities in order to make it impossible for Tehran to make nuclear weapons -- an ambition it denies.
But the Islamic republic wants to expand its activities, most notably its capacity to enrich uranium -- a process which makes reactor fuel but also, potentially, the core of a nuclear bomb.
"I promise the Iranian nation that those (enrichment) centrifuges will never stop working," President Hassan Rouhani vowed Monday, calling UN and Western sanctions "tyrannical".
'Fools to walk away'
"Extending is not going to make it easier," former US State Department official Mark Fitzpatrick, now at the International Institute for Strategic Studies in London, told AFP.
"The problem is that there are fundamental differences. Iran is not willing to accept what would be required (for a deal)," he said.
So why have the army of officials, experts and diplomats, shattered after 10 rounds of talks -- chief US negotiator Wendy Sherman has made clear she is tiring of Viennese speciality Wiener Schnitzel -- bothered putting more time on the clock?
The reason is quite simple. The alternative -- a collapse of the talks and a return to the explosive situation before last November's interim deal -- is far worse. Kerry said the parties would be "fools to walk away".
Before the November 2013 accord kicked in, Iran was enriching uranium to close to weapons-grade, the West was applying more and more sanctions and the danger of Israeli and US military action was growing.
Signup to our newsletter and follow us on Facebook and Twitter!
Obama under pressure
Now, key parts of Iran's programme are frozen, meaning that, unlike before, the country is no longer creeping ever closer to potentially creating a bomb. In return, it receives around $700 million every month as overseas assets are freed up. This will continue until July.
"If either side decides to walk away, the consequences will be catastrophic," Kelsey Davenport, analyst at the Arms Control Association, told AFP.
"As long as Iran's programme remains capped and the sanctions remain capped then both parties are better off," agreed Fitzpatrick.
"Seven months is longer than anyone expected, but the longer the better."
But the extension carries the risk that critics in both Iran and the United States might lose patience.
Israel -- the Middle East's sole if undeclared nuclear-armed state -- and Gulf states are also sceptical.
Meanwhile, hardliners are waiting in the wings to undermine Rouhani, who has little to show in terms of boosting the Iranian economy from his strategy of sealing a rapprochement with the West.
But the bigger danger is for his US counterpart Barack Obama, with opposition Republicans in control of both houses of Congress from January.
No sooner had the extension been announced Monday that several Republicans advocated more sanctions.
"Now, more than ever, it's critical that Congress enacts sanctions that give Iran's mullahs no choice but to dismantle their illicit nuclear program," said Senator Mark Kirk.
But more sanctions -- Obama's veto could be overridden if enough rebel Democrats support new sanctions -- would be a breach of last November's interim deal and could prompt the Iranians to walk away.
"We should give the negotiators as much time as they need to finish their work," said Ali Vaez from the International Crisis Group.
"Enormous progress has been made. This is now too big to fail."