It was the American screenwriter William Goldman who said famously: "Nobody knows anything."
He was talking about Hollywood. But he could just as easily have been talking about North Korea.
And that is the big problem when it comes to America's dealings with the most reclusive, secretive, duplicitous state on earth. Successive attempts over the years to persuade the regime to dismantle its nuclear programme have foundered on the whole question of proof or verification.
:: Trump v Kim: Who said what?
The long, drawn out Six Party Talks, which lasted from 2003-2009 and involved the US, North Korea, Japan, China, Russia and South Korea, showed promise at one stage.
But then they collapsed when it came to North Korea's reluctance to be transparent. Openness is anathema to them.
:: North v South: A tale of two Koreas
Both Kim Il Sung and his son Kim Jong Il began processes which promised denuclearisation in return for the easing of sanctions, and both used the same strategy. Delay, procrastinate, buy time, but ultimately do not deliver.
To them the development of nuclear bombs was the key to prolonging the life of their rule. To the Kims, regime survival is everything.
The Trump administration – confronted with missile tests and other provocations – imposed tighter sanctions and then traded threats and insults with North Korea.
When the regime suddenly did an about turn and offered to send athletes and officials to the Winter Olympics in South Korea, the American instinct was that the North Koreans were up to the same tricks: reaching out and making commitments they knew they would never keep.
2:52But there is an outside chance, that this time the overtures from Kim Jong Un – unlike his father's and grandfather's – are genuine.
He might actually be prepared to give up his nuclear weapons. He just may have calculated that the best way to survive is through economic strength rather than through nuclear capability.
Furthermore the fact that he now has nuclear missiles capable of doing damage to his neighbours and the US means he is in a strong position to bargain.
Certainly the South Koreans are cautiously optimistic that this is the Kim strategy. And so too is an American diplomat, Joseph DeTrani, who took part in the Six Party Talks and who senses that Kim Jong Un has decided that if he gets security guarantees from the US and financial help from China, South Korea and Japan, then that would better protect his regime than keeping nuclear weapons.
"I think he has decided that is his strategy and denuclearisation is a real possibility," Mr DeTrani told me.
3:16It may just be that that is Trump's calculation too. Why else would he invite Kim Jong Un's henchman and top intelligence officer to the White House? Mike Pompeo, the Secretary of State, has made two visits to Pyongyang and also seems convinced that the North Koreans are serious.
:: Guide to the Trump-Kim summit in Singapore
It is why Trump may just have found himself in the right place at the right time. The self-professed "deal-maker" may actually have a deal to do here.
But as well-intentioned as Kim Jong Un may be, it will be difficult for his regime to overcome decades of suspicion of outsiders and fear of opening up. Secrecy, brutality and double-crossing are deeply ingrained in their thinking.
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A former CIA analyst on North Korea, Su-Mi Terry, told me that the North Koreans have so many hidden facilities, tunnels and hiding places that it would be impossible to verify exactly what is going on. She believes that the issue of verification and proof could again be the rock on which Trump's quest for a deal crashes and burns.
The North Koreans may promise to do something. Proving they've done it will be a very different matter. Whatever happens any agreement will take years to complete. But that is no reason for Trump not to try. The signs have possibly never been better for a deal.
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