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.