By Paul Reynolds
World affairs correspondent, BBC News website
Mr Clinton was welcomed upon his arrival in Pyongyang
It would be wise to adopt the precautionary principle when thinking about the implications of Bill Clinton's visit to North Korea.
The former US president might well have obtained the release of the two American journalists held by the North Koreans.
But it is impossible to be confident that North Korea is suddenly going to change the policies that have resulted in its ability to explode a nuclear device.
Optimists will point to the changed atmosphere since the election of US President Barack Obama, who has dropped the "axis of evil" talk of his predecessor, George W Bush.
And the fact that Bill Clinton has gone perhaps indicates a readiness by North Korea to discuss something wider than freedom for two reporters.
It was on Mr Clinton's watch as US president that an agreement was reached - though later abandoned - to freeze the North's nuclear weapons programme.
However, even if there is some movement - such as the North agreeing to rejoin the six-party talks on its nuclear activities - the question will be how long that change will last until the next reversal.
With North Korea, it is usually one step forward and two steps backwards.
Kim Jong-il has moved North Korea towards a military-first policy
There have been similar rescue missions to the North before and they did not impact on the strategic position.
Authoritarian and dictatorial regimes often like to be courted and asked for favours. Sometimes they grant them and then continue as before.
In 1994, Bill Richardson, then a US congressman, was in Asia on a congressional visit when a US army helicopter was brought down on the wrong side of the demarcation line.
Mr Richardson managed to persuade North Korea to free the surviving pilot and release the body of the other. But the US had to issue a statement of "sincere regret" at the incident.
Not long afterwards, Mr Richardson got the release of two Americans from Iraq, then ruled by Saddam Hussein. It was said that no deal was done and certainly the Iraqi leader's policies did not change.
In 2007, we saw Iranian President Mahmoud Ahmadinejad smiling and shaking hands with 15 British sailors and marines seized in the Gulf. Iran carried on with its nuclear policies anyway.
The most important intervention with North Korea was carried out in 1994, not for humanitarian reasons, but for reasons of international security.
At the time, just before Mr Richardson's mission, North Korea was forging ahead with nuclear development. The US seriously feared that a war would break out on the Korean peninsula.
Mr Carter's visit in 1994 led to an agreement on nuclear weapons
Mr Clinton asked former president Jimmy Carter to see the then-North Korean leader, Kim Il-sung. Mr Carter got a result.
The North agreed to freeze its nuclear fuel reprocessing and this eventually resulted in an agreement in Geneva later that year.
However, over subsequent years, and under Kim Il-sung's son, Kim Jong-il, North Korea has moved towards a military-first policy.
This even has a name, "songun", and it emphasises that nothing should come before military strength in its domestic and foreign policy.
Since then, the North has left the Nuclear Non-Proliferation Treaty and has exploded nuclear devices.
Maybe it is now ready to change. Maybe not.