4 ideas
The narrator is born around the 2008 Beijing Olympics, and China's twentieth century then unfolds around him in reverse: an affluent childhood, market reforms and the 1989 protests as he comes of age, then the Cultural Revolution and the Great Famine in middle age. His life therefore runs from abundance toward catastrophe, and he, his friends and his loves must adapt to each harsher era as it arrives.
The same set of events reads as a story of progress or of collapse depending only on the order in which they are lived. Running the chronology backward strips out the built-in 'things got better' ending. Each catastrophe then has to be judged on its own terms rather than excused as a stage on the road to prosperity.
Individuals take the conditions of their own moment as the baseline for ordinary life. They adjust their ambitions, fears and moral compromises to it, whether it is an age of plenty or of political terror. Personal fate is therefore set less by character than by where one's lifespan happens to fall along the historical timeline.
Taken from Pushkin's line that what has passed will come to seem dear, this idea holds that memory softens earlier times whatever they actually contained. Nostalgia comes from the rememberer's position in time, not from the quality of the era remembered. The novel exposes this by letting the narrator look back fondly on prosperity while living through suffering.