In Hanoi, they call it the 'China factor'.
Unique among its South East Asian peers, in Vietnam no major decision is made without considering the impact on its complex relationship with its giant neighbour, according to officials and scholars.
And that even extends to the leadership of its Communist Party and government - decisions the party will finalise over the next week at its first congress in five years.
While outwardly pro-China candidates are simply not an option, amid security tensions that have seen Hanoi court its cold war enemy, the United States, neither are leaders likely to be overtly hostile to Beijing.
'The lessons of our history have created some hard realities for us,' said one Vietnamese official recently. 'We need leaders who can stand up to China and defend our sovereignty. But we also need to have a full and deep relationship with Beijing ... when you look at our borders, you will see there is no escape. We have to think constantly about balance.'
That history has left contradictions that bedevil the relationship today. Centuries of Chinese domination and Vietnamese rebellion have created cultural and political similarities as well as deep mutual suspicions - tensions that exploded into a short war as late as 1979.
In the current environment, that means Beijing and Hanoi - the largest of the world's remaining Communist Party-ruled states - increasingly foster political, cultural and economic links. Hundreds of delegations - from secret police to agricultural officials - visit each others' capitals each year.
Yet at the same time, Hanoi has at times alarmed Beijing. It has, for example, been instrumental in deepening Washington's engagement with South East Asia through the Association of Southeast Asian Nations - a drive that reflects Vietnam's deep-set fears about China's military build-up and the worsening of its South China Sea dispute.
The Congress - traditionally an act of tightly-choreographed political theatre - will not debate such issues in any detail, but instead essentially rubber-stamp policies and leadership changes hammered out largely in secret by the party's 160-member Central Committee.
With the party long favouring continuity and a glacial pace of change to any radical shifts, no-one is expecting glaring policy turns.
Most noticeable will be confirmation of a new ruling troika at the top of the 15-member Politburo to lead the country for next five years.
The dynamic Prime Minister Nguyen Tan Dung, 61, is expected to stay on, but will serve with a new Communist Party chief and state president, in keeping with Vietnam's tradition of a collective leadership split across various factions and backgrounds that means no single leader has absolute power.
Current party chief Nong Duc Manh, now 70, must retire and is widely expected to be replaced by current legislative head Nguyen Phu Trong, 66. Some have described Trong as pro-China - a description that appears to miss vital nuances.
Veteran politburo member Truong Tan Sang, 61, is expected to replace Nguyen Minh Triet as president. A key party administrator and a former party boss in Ho Chi Minh City, Vietnam's largest and richest city, Sang is thought to have wide regional connections, particularly solid in Japan.
Such a line-up reflects the need to maintain a course of standing up to China where needed, but avoiding outright hostility, according to veteran Hanoi military and political analyst Professor Carl Thayer, who is based at the Australian Defence Force Academy in Canberra.
'There is no-one in the leadership now who is overtly pro-China as in the past,' Thayer said. 'Anti-China sentiment is now pervasive throughout the various ruling elites.'
Yet Beijing would, nonetheless, find a new regime it could do business with. 'You have to always remember Vietnam's relations with China are far more important than all its other relations ... and that will be reflected in the new line-up,' Thayer said. 'Nothing happens in Hanoi without careful consideration of the impact on the China relationship.'
While Hanoi's emerging strategic partnership with Washington will continue, progress will be gradual, given Hanoi's habitual caution.
'There is still not much substance in the relationship,' Thayer noted. 'It is pregnant with opportunity, but at this point it is still mostly symbolic.'
Trong, once the party's key theorist, is a relatively conservative figure who will be well understood in Beijing. He will lead the fraternal side of the relationship with China's leaders. One Asian diplomat with long experience of both countries noted that Trong, known as a mild-mannered, amicable figure, would probably be able to work smoothly with Dung, who wants to attract more Chinese investment into Vietnam.
For some years mainland investment in Vietnam has been largely conspicuous by its absence compared with the rest of South East Asia, in part reflecting mutual suspicions.
Dung's recent approval of a Chinese bauxite mine drew rare public criticism and concern from delegates at the National Assembly, who accused him of selling out the country's environment to the Chinese.
'While it is clear Vietnam will be holding the line after all its efforts to stand up to China over the past year or two, I don't think Beijing will be too concerned with this line-up ... the more positive elements of the relationship look quite secure,' the Vietnamese official said.
Significantly, Defence Minister Phung Quang Thanh is expected to stay on, reflecting a widespread desire for continuity after a year that has seen Vietnam embark on unprecedented military diplomacy to internationalise the South China Sea. The Defence Ministry, too, has successfully lobbied for approval for its most ambitious arms purchase yet - six state-of-the-art Kilo Class submarines from Russia, widely seen as a vital deterrent to China's navy.
The select few
Vietnam's Communist Party Congress elects a Central Committee of: 160