For more than a century, China's desire to bring Hong Kong and Taiwan fully into its fold has been thwarted by various events: opium, conflict with Japan, civil war.
Now, add two more items to that list: an elderly bookseller and a teenage K-pop starlet.
They have weakened the two constructs - One Country Two Systems and the 1992 Consensus - which in recent decades had undergirded China's engagement with the two islands. With the latest developments, China's relations with Hong Kong and Taiwan, never easy issues for the Chinese Communist Party (CCP) government, look set to be trickier than ever.
The curious disappearance of 65-year-old Hong Kong bookseller Lee Bo and the similarly curious apology by 16-year-old Taiwanese girl band singer-dancer Chou Tzu-yu could not have been timed better by critics of Beijing looking to poke holes into its handling of the Greater China periphery.
First, two days before New Year, Mr Lee vanished from the streets of Hong Kong. A partner in a publishing firm specialising in gossipy political paperbacks about China's leaders, he was widely suspected to have been snatched by Chinese state security agents.
If so, this would have been a clear breach of the city's mini-Constitution Basic Law, which states that the city has its own laws and enforcement powers. Even Hong Kong Chief Executive Leung Chun Ying, while obsfucating on whether Chinese officials had indeed overreached into the territory, said such actions would have been "unacceptable".
In what appears to be instructed attempts to stem speculation, the bookseller sent various missives saying he had travelled to mainland China on his own accord to "help in investigations" and urged supporters not to kick up a fuss.
Less than three weeks later, it was the turn of pop ingenue Chou to deliver a scripted message. Dressed in a funereal black turtleneck, her back to a wall and reading from a prepared statement, the teenager put out a self-denunciation, just before Taiwan's presidential and legislative elections.
For the act of waving a flag of the Republic of China (ROC) - Taiwan's formal name - in an online video, she was "very, very sorry", she said.
"There is only one China," she said sombrely. "Both sides of the Taiwan Strait belong to the same entity. I have always thought of myself as a zhong guo ren (Chinese citizen), and I am proud of it."
The apology, many Taiwanese believe, was coerced, perhaps by her South Korean management company under the pressure of Chinese clients and fans. Chinese netizens had earlier reacted angrily to Chou waving the flag, accusing her of advocating Taiwan independence.
ONE COUNTRY, TWO SYSTEMS?
So how did these episodes inflict so much damage to One Country Two Systems and the 1992 Consensus?
They essentially exposed the limitations, if not hollowness, of the two doctrines.
Both were deft diplomatic manoeuvres which - in their deliberate rhetorical vagueness - offered a semblance of meeting of minds, by allowing either side to focus on what they wish.
Not coincidentally, both phrases are bifurcated to facilitate this ambiguity. One Country Two Systems (yi guo liang zhi), for instance, was created by the late Chinese leader Deng Xiaoping in the 1980s as a way to court Taiwan. It later was adapted to Hong Kong in the run-up to its return to Chinese rule in 1997, and went a long way in assuaging panic in the city and among global investors.
While Hong Kong is now part of China - "one country" - the city will retain its own system and way of life, the policy reassured. "The horse races will continue, the dances will continue, and, so too, the stock market," Deng declared then. Hong Kong will be governed by Hong Kongers, enjoy "a high degree of autonomy", and there will be "no change for 50 years". The central government's role is restricted only to the city's defence and foreign affairs.
Uncomfortable questions, such as how "high" this degree of autonomy is or what happens when "one country" clashes with "two systems" , were not examined too closely in the interests of seeking common space.
But the alleged political kidnapping of Mr Lee on Hong Kong soil is now a hard swing at this carefully crafted veneer of harmony.
While Beijing's hand in Hong Kong affairs had become more visible in recent times, especially after the Occupy movement in 2014, it was largely in areas where interference could conceivably be justified and explained away - the government, media, academia.
An abduction of a Hong Konger, possibly by the Chinese security authorities working beyond their legal remit, is something else and has raised perturbing questions about the city's future, including its most fundamental value - the rule of law.
It was perhaps in cognisance of the damage done that a theory is now being floated in Beijing-friendly quarters - that the kidnapping was carried out by "rogue" agents without the sanction of the top leadership. Another explanation is that it was related to a power struggle within the CCP, with different factions using the booksellers to propagate unsavoury information about their rivals.
Others are distancing themselves: China's legal representative in Hong Kong, Mr Wang Zhenmin, has been reported as expressing concern over the matter. Guangdong governor Zhu Xiaodan has said he believes there will be "a practical and fair judgment" for Mr Lee's case.
But whatever the denouement of this saga, damage has been done to the credibility of the One Country Two Systems policy.
Meanwhile, the 1992 Consensus, which had propped up cross-strait relations for the past eight years, is also teetering.
It was coined to describe a tacit understanding reached between Beijing and Taipei in 1992 that there is One China, Different Interpretations (yi zhong ge biao) - one that Beijing holds sacrosanct.
Essentially, this allows both sides to agree that China and Taiwan are part of one country - China - but with different ideas of what that "China" means. Beijing takes it to refer to the People's Republic of China (PRC) under the CCP, while Taipei under the Kuomintang (KMT) interprets it as the ROC established by the KMT which fled mainland China for Taiwan in 1949 after it lost the civil war.
Taiwan's pro-independence Democratic Progressive Party (DPP), meanwhile, adheres to Beijing's view: that there is only One China and the PRC is that China. But it does not believe that Taiwan is part of that China.
This is a view that is gaining strength in Taiwan, where the rise of the Taiwanese identity means that more and more are rejecting the idea that their island is part of the Chinese entity.
The Chou episode, erupting on the day that Taiwan went to the polls, helped seal the deal for the DPP. A survey later showed it had swung about 10 per cent of votes in favour of the DPP, which clinched both the presidency and an unprecedented parliamentary majority.
That night, in an emotive victory speech, President-elect Tsai Ing-wen pledged: "As long as I am president, I will do everything in my power to ensure that no citizen of Taiwan will need to apologise for their identity."
More than the immediate dividends to the DPP, the flag-waving affair undermined - perhaps fatally - the brittle edifice that the 1992 Consensus is mounted on. The irony is that the ROC flag that Chou brandished is, in fact, a formal symbol of Taiwan's links to China, an emblem of the Republic founded in 1912 by KMT on mainland China.
In Taiwan, it is thus waved by KMT and other pan-blue (pro-unification) supporters; it is viewed with ambiguity by the pan-green (pro-independence) camp who prefer the DPP's green flag imprinted with the shape of Taiwan and the term Republic of Taiwan. By mistaking the ROC flag as a symbol of Taiwanese independence, Chinese netizens have given ammunition to the pro-independence camp's argument that the 1992 Consensus is a farce: China respects just the "One China" half of it and pays mere lip service to the second half - "Different Interpretations".
It had also, as one observer noted, allowed Ms Tsai to "co-opt the ultimate China motif into a pro-independence narrative", as she defended the right of the Taiwanese to use the ROC flag.
Post-victory, she made it clear that she will be no champion of the 1992 Consensus; while she "respects" its spirit, a new formula for cross-strait co-existence, she said, has to be found.
The upending of the twin principles thus spells trouble for China as it tries to maintain its grasp on Hong Kong and Taiwan.
Unsatisfactory as they are, One Country Two Systems and the 1992 Consensus were perhaps the best compromise that could be conjured in their day. But their success depends on goodwill on all sides to keep up their end of the face-saving bargain.
Now, the mask has been torn off and what has been exposed are the stark differences beneath.