If there is an unspeakable c-word at the sharp end of northeast Asian affairs, it is 'contingency'. Delve into security issues bedevilling the Korean Peninsula - the world's last cold war frontier - and it quickly becomes apparent that the issue of how the region's powers would react should North Korea one day implode is exceptionally sensitive. So sensitive, in fact, that the big players struggle to address the issue, despite its obvious dangers.
As one veteran regional envoy put it recently: 'It's ... exceptionally difficult to discuss - the elephant in the room, you might say. And that tells us a lot about the way the region works, or doesn't work.'
The US and South Korea, he explained, plot contingencies among themselves, as part of their active alliance that still involves some 28,000 US military personnel based south of Seoul.
To a more limited extent, the US and Japan discuss scenarios. But specific Japan and South Korean discussions remain in their infancy.
And China, as Pyongyang's remaining fraternal ally and lifeline, largely remains a closed book to the other three.
Others involved in the troubled six-party process to rid North Korea of its nuclear weapons programme say that, despite early hopes, the effort has done little to boost trust among the other five - China, US, South Korea, Japan and Russia.
'The shutters just come down when worst-case scenarios surface, even privately,' a Japanese diplomat said of Beijing's habitual reserve.
Terrifying scenarios are not difficult to imagine, of course - US-backed South Korean troops and Chinese troops pouring over their respective borders and meeting on disputed ground. Then there would be the need to secure the North's nuclear facilities.
Preventing such a situation from degenerating into a modern version of the Korean conflict of the 1950s is looming as a major challenge for the region's intelligence agencies - the institutions able to maintain and foster off-the-books conversations.
The sources of sensitivity are not hard to find. Beijing has repeatedly shown itself loathe to even criticise its fraternal neighbour, despite the many frustrations prickly Pyongyang inspires.
When WikiLeaks cables in late 2010 quoted US officials suggesting Beijing would ditch Pyongyang if it collapsed, mainland military and diplomatic experts were swift with their condemnation.
South Korea, too, is officially wedded to a policy of gradual and peaceful unification and avoids discussion of collapse, while renouncing ideas of a forced takeover. That does not mean, however, that it doesn't want more co-operation and input from China over dealing with its northern enemy.
For all the propaganda pumped out of Pyongyang to buttress the fledgling rule of Kim Jong-un, the nature of his regime - cheating history as the world's last Stalinist hermit state - remains fundamentally unstable.
As cunning and as cryptic a regional player as Pyongyang is, it has so far not extended those smarts to the reforms that have taken root in China or Vietnam. The threat of sudden collapse, therefore, cannot be ignored.
Greg Torode is the Post's chief Asia correspondent. email@example.com