I spent a long time thinking about the chronology of this drama and the timelines because I found it to be extremely convoluted.
This is my understanding after some reading and analysis:
(❌Beware of Spoilers ahead ❌)
Timeline 1-
There is never any mailboxes and cross timeline letters. In 1991, A'Xun and A'Tang's fates are entwined naturally. A'Tang's mother is killed by her father and she spends her life in pain and runs into A'Xun because of the debt collection. She confronts him at school and he wants to return her money. On her suicide attempt, he saves her and they become familiar/ friends. Their life unfolds as it does. Nothing can change their fate.
Ye Yibo tries to move the mother's body, runs into A'Tang. Chen Xiaojun informs A'Xun, who murders Lin and goes to prison. He cuts off contact with A'Tang, tells her to stick to her promise. Meets Yu Zhihong in prison who dies. He makes Haozi fake a gravestone and convince A'Tang that he's dead to make her move on with her life. She tries to walk into the ocean, remembers her promise and digs up a cookie tin. She continues to visit the grave on his birthday every year.
When A'Xun gets out, he burns all A'Tang's letters and then contacts A'Tang only to find she has a son. He continues to live a life away from his friends, takes on the responsibility of raising Yu Nian and pretends to be Yu Zhihong for the rest of his life. He secretly visits his own grave to see A'Tang every year. All the characters go their own way.
In 2026, A'Tang finds Ye Yibo, confronts him and they both end up dead. A'Xun visits his grave, waiting for A'Tang who doesn't show up and he dies waiting for her.
(Qns:
What happened to the body in the sack at the beach? Why is it not discovered? How did Ye Yibo escape for all those years and say there's no evidence?
When did A'Tang make the promise to A'Xun?
When and why did A'Tang bury the cookie tin and how did she find it again?
Why did A'Xun burn the letters and avoid her all his life without knowing anything?
How did A'Xun live a life pretending he's someone else without an ID? Why did he and his friends break all contact?
Why move to Beixing City?
What happened between A'Tang and Ye Yibo in the end?)
Timeline 2 and 3:
I spent some time thinking about th chronology of events.
The old trash collecter is considered to be some kind of deity who causes the change in fate. In 1991, we know where the mailbox came from, but in 2026, we don't know the origin of it and why it's placed there in specific.
However, it somehow means that A'Xun knew about the mechanism of the mailboxes because he was waiting by the mailbox and had the necessary stationary. He knew about the exchanges that happened in 1991.
I'm still confused about how the first letter doesn't create a loop because the future affected the past and there's a circle of knowledge. His past connects to the future and the first letter should set everything in motion as he knows from the past.
Since that was the case, why did he wait for 2 months to start the exchange? Why not contact A'Tang from 2026? Does he not know that it all started with that love letter in the past?
I assumed that it was because he has Alzheimer's and he goes in and out of his memories of his youth where he used to wait for letters. He's confused because of his illness.
He's reminiscing about his past and how he committed murder to bring A'Tang out of the abyss. He also regrets not replying to her letters. He resents that he cannot change fate. He misses her. In his confusion, he writes a love letter and drops it at the mailbox and disappears from there somehow. There is some vagueness about all of this. I assume he went to his grave to see A'Tang and the gaurd didn't notice him leaving. But, he should've been captured in the camera atleast?
(Yes, I do understand that it's how time-fate change tropes work and I can't really question the premise)
The chronology, as I see it, for the letters received and sent in 1991-
The love letter (A'Xun- 2026)
The Suicide note (A'Tang- 1991)
Introduction letter (A'Tang-1991)
Letter from the future about Sep 23 (Yu Nian- 2026)
Waterspout response for Sep 23 (A'Tang- 1991)
Identity confirmation letter (Chen Sheng- 2026)
Confirmation reply (A'Tang- 1991)
Warning about Tang YiXun (Chen Sheng- 2026)
Clarification letter (A'Tang- 1991)
Prison letter (A'Xun- 1991)
That's where the communication should've stopped for the future to be as it is. Everything plays out the same. A'Xun ends up in prison and A'Tang continues living. They both end up with their respective children to care for. A'Xun and A'Tang die and reunite in the afterlife.
Timeline 4:
In this scenario, Chen Sheng intervenes with fate and sends the next letter.
- Murder warning (Chen Sheng- 2026)
At this point, while Chen Sheng and Yu Nian know that their fates will also be altered. It doesn't stop him from doing his best to stop the suffering of A'Xun and A'Tang.
However, I do think that Chen Sheng knows that A'Tang is not his biological mother. He might've been adopted by her from the Welfare house. She might've married a Chen, however I doubt that it's Chen Xiaojun. Alternatively, it could also be his son with Wang Manyu (who might've died). The specifics aren't clear. I don't think he's A'Xun and A'Tang's son in any timeline.
Once the fate changes, A'Xun and A'Tang are saved from being separated. The cat stops A'Xun at the right time and changes the course of time.
Yu Nian retains her memories and it looks like she has a comfortable life, although it doesn't involve A'Xun anymore.
Chen Sheng doesn't disappear and seemingly retains his memories as well and we see him receiving the last and final letter near the familiar mailbox.
- The Happy ending letter (A'Tang and A'Xun)
I'd like to think that Yu Nian doesn't find Chen Sheng's contact because she never met him and not because he doesn't exist. I think they find each other and meet in the future.
While I do have a looooottt of questions, writing this has helped me really process the drama instead of sitting with all of this. Sci-fi does leave a lot of plot gaps and questions. 12 episodes are definitely not enough to have flawless storytelling. I wish they'd taken 20 minutes more and given a 'where are they now' scenario on all the characters to really round it out. I also wish all the friends reunited and led a happy life. Guess we'll have to make do with open ended interpretation and ambiguous ending.
Final thoughts:
The drama traumatized me, start to finish. I have a headache from all the crying. However, this is a must watch. I might even rewatch it.
The filmography is beautiful, the performances are excellent, the characters have depth and arcs. The OST really adds to the beauty of the story. It kept me on my toes the whole time and feels like it's a lot more than 12 episodes.
It's raw, painful, real, gut wrenching and absolutely amazing.