Translation is done from Vietnamese to English. Large thanks to 和平, the admin of the discussion group on FB, for translating from Chinese. I did a bit of rewrite to hopefully make it flow better but maintain the same idea. 

Some spoilers are in here so skip that if you don't want to read it.

NB: Detective here as in drama using logical deduction, not necessarily an actual one. The Vietnamese word for time-traveling film also contains crossing through dimensions. 

Interview: "The role was written for Alice Ke and the writers have strong belief in Greg Hsu's prospect"

Q: Netizens asked "How did the scriptwriters be able to write such an amazing script? What are the thought process behind it?"

A: Although Chi Feng Chien (简奇峰, scriptwriter 1) always referred to his dream as the source for initial concept in older interviews, the development for this drama went as far back as 2012, after his collaboration with director Tien Jen Huang (黄天仁) for “What is Love”. The two discussed what the next drama would be about and the director wanted to do a “detective”* drama. CFC said that it’s very normal for him to discuss about the next project with people he enjoyed collaborating with. He also asked Ma Yi Ting (麻怡婷, previously produced Alice Ke’s Marry Me, or Not) about this and MYT wanted a drama that “suddenly makes people tear up”.

CFC started to develop concepts with these discussions in mind and on one day, it came to him in his dream, in which he was chasing a script deadline.

The script within the dream was about a couple who broke up. Not long after they broke up, the girl passed away. Each episode reveals events before and after she was gone and it is only until the final episode that the audience understands why they loved each other and why they had to be separated.

After he woke up, he talked to Hsin Hui Lin (林欣慧, Scriptwriter 2) and she rushed him to write the script, “This is the script your future self sent to you”.

“But I am not dead yet. Why do I have to send this dream to myself?” – CFC said.

“But what if you are not going to finish writing in time? You’re going to regret it after death”. And that’s how Someday or One Day was born.

Q: While writing, was there anything that you find difficult to grasp? Was there anything that caused arguments? (spoiler)

A: During the writing, the only thing that we (between the 2 writers) argued about was Xie Zhi Qi’s time travel. HHL said that letting the perpetrator time travel was a fresh idea, but was going to break the beautiful concept of “time traveling because of the wish to see the other person”. However, she finally stepped back and agreed to this new idea.

Although viewers have difficulty understanding at times as the drama gradually pieces time and space together, the scriptwriters’ intentions were very clear.

“The person who we need to convince is not the director but everyone, especially episode 7. We didn’t see any issues while writing, but everyone will feel as if the world is going to be destroyed when these souls meet.” 

The viewers might be limited by their previous experience of watching time-travelling films so the writers wanted to break that mould and created a set of rules that belonged to “Someday or One Day”.

At the end of the script, the 2 writers and director also argued over the plot point that Mo Jun Jie has never believed in Huang Yu Xuang’s time/dimension-travel. CFC explained: “The director believed that MJJ liked Chen Yun Ru, so he had to recognise who she was, but for me, he had never believed her.”

After the argument, CFC, although understood the director’s wish to protect MJJ the character, explained:

“I want to protect the plot even though I’m very grateful for the director while developing the script. During writing, it was hard to explain to people about these dimensions in the shortest amount of time. However, it was the definition of Mobius strip brought up by him that this idea was quickly formed.”

Q: Why did you ask Alice Ke and Greg Hsu to play the lead? 

A: We wrote the character based on Alice Ke as we had worked with her in the past. “Alice Ke have both HYX and CYR’s characteristics”. In other words, they seek her out for the collaboration. On the other hand, MYT suggested inviting Greg Hsu but it wasn’t certain as Greg Hsu was very new and was worried that the general public wouldn’t accept it.

When hearing about Greg Hsu, CFC laughed “I definitely believe he will be famous!”. Because as it turned out, Greg Hsu went to the casting audition for “Attention, Love!”.

 “When he stepped in the room, that closed space was filled with female hormones (aka. all attention was on him). I felt as if this space didn’t belong to me, my existence is like an eyesore, hindering everyone and at that moment, I felt the attractiveness of Greg Hsu.”

 (t/n: I died laughing translating this. But thank you for so much for seeing his potential ;___;)

It was a shame, the scriptwriters thought, that Greg Hsu couldn’t get the main role but they did think that they would give him a chance to be the male lead in the future. Finally, his acting didn’t let everyone down and he showed a clear difference in his acting as a character within large age range.

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More info:

1. The drama was prepared for 3 years and was filmed from 27/12/2018 to 10/5/2019, 13 episodes were filmed in 115 days. (t/n: this is probably why the lack of trust in inviting Greg Hsu by the producers as he really didn't have much substantial work until last year. Though I wonder why considering Kai Ko's "You're the Apple of My Eyes" was his first movie ever, while Greg Hsu was struggling for years).

2. Last Dance is the scriptwriter's favorite song from Wu Bai and it was not popular. People don't pay attention to B-side as much, just like how people don't pay attention to CYR, so very fitting to this drama. This is also why the characters can listen to this song right after putting the tape in, since this song is the first song on the B side of the album "The End Of Love".

3. The English title "Someday or One Day" can be explained: someday refers to a day in the future, while one day can be used for both past and present, so the title shows a possibility that the past is the future and vice versa. 想見你 (Want to See You) doesn't stop at just a day but from the past to the future and backward.

4. This drama is not only a love story, but about helping the lost souls.

5. The scriptwriter has a habit of using real people's names in his work. Wang Quan Sheng was his primary school's classmate, HYX and Li Zi Wei are both his high school's classmates, completely unchanged. 

Xie Zhi Qi is the writer's dentist, might have changed the surname. He is scared of him. =)))))

6. People asked if the audience would get sick listening to Last Dance being repeated in the drama, the writer said people shouldn't worry because he has been playing it for more than the last 3 years and he hasn't vomited yet. =))))))

7. If you read my other comments, Greg Hsu was really only allowed to be the male lead through MYT's suggestion because Alice Ke was also in it. They needed a popular star with good acting to guide him and to bring in the rating. Mo Jun Jie's character required casting audition and the director's vote got Patrick the role. 

8. Tainan has a lot of great food so Patrick Shih gained weight while filming. He got told off by the director until Yan Yu Lin joined the cast. 

9. If they are allowed to play any roles regardless of genders, Alice Ke wants to play WQS while Greg Hsu and Patrick Shih want to play CYR.

10. Alice Ke only had eyebrows drawn when playing high-school scenes. 

11. The plot point about the lost hearing aid was explained in the script but got cut due to time restriction so they only left it to HYX to say it in the precinct.

12. The production team had no budget for promotion in Mainland China (t/n: The media very much credited its success to the prolong break and also word-of mouth)

13. The team said that SDOD cost 1.5 times more than the usual idol dramas but is less expensive than "The World Between Us". So it can be calculated that each of the 26 episodes (shown in China) cost around 350k RMB. Greg Hsu's total salary is rumored to be around 150k yuan, which is said to be even less than that of an assistant of a trending star in China. Netizens either react saying they understood why Taiwanese stars want to crossover and side-eyeing their own stars who earned so much but never got better at acting.

14.  The production team very much insisted on following the script as it was intentionally written. They didn't let the investors or the network interfere with the production and even rejected having advertisement on the TV screen.  

15. For Chen Yun Ru's character visual, the scriptwriter and the production team suggested having her wear a mask to differentiate her from HYX but the director hoped the actress would make this distinction from her own acting. (He is very right and the result is just as we see)

16. The director and the production team had a fight as the filming was going over budget and they said they would have to pay up for the cost. The 2 sides didn't talk to each other for a week. 

17. There's a cat-killing scene in the drama but in real life, Yan Yu Lin is a cat person, who always carried cat food around to feed stray cats and recently adopted one ;__;

18. Number 32 is chosen as it has interesting meaning (I don't know what it is and the writer didn't explain I assume).

19. 831 wrote the ending credit "想見你 想見你 想見你" after just watching one episode and from the drama's title. 

20. There's a lot of award-winning people involving in this drama. Shi Shi (songwriter-singer for the OST Someday or One Day and Come Away) just got an award for best album last year. Alice Ke, Yen Yi Wen (CYR's mother) and the policewoman are Golden Bell-winning actresses. Yen Yi Wen co-directed "The Making of An Ordinary Woman" and is possibly going to be the direct competitor of SDOD in this year's Golden Bell. If you noticed her MDL's page, she really worked on some of the best Taiwanese dramas recently. 

T/N: Please leave me a thanks because it really took me a while to translate this, at 2:45 am. =)))))))The spoiler bit is very interesting, though sounds disappointing but actually makes sense the more I think about it, esp in correlation to episode 13. I will translate another interview of his later.

You really did a lot of work. Thank you for this. I wasn't able to find any interview or behind the scenes with eng sub but i feel happy after reading this. 

@Woorie, it’s my pleasure. I really love this drama and hope everyone will see how much dedication the team have put into this.

 Chi Nguyen:

@Woorie, it’s my pleasure. I really love this drama and hope everyone will see how much dedication the team have put into this.

The team really put a lot of hard work and dedication to create such a wonderful masterpiece and as a result we all love it.

Loved this list! Thank you for the hard work.
It's worth noting too that Greg Hsu first appeared in Jay Chou's "Class 3-2" music video back in 2003, which is the same class he and Patrick are in (Year 3 Class 2?), and coincidentally the same number that appears through the whole show. But there could be another meaning behind it.

''Xie Zhi Qi is the writer's dentist, might have changed the surname. He is scared of him. =))))) '' bahahaha, that made me burst out laughing. Thank you so much for translating! I love how this idea came to him in a dream, makes it even more special. You could feel this show was written with soul, rather than for commercial purposes. I was also really curious how the title related to the show, but I got my answer now :D

I've also seen Attention, Love! but I can't believe I didnt realize greg hsu was in it until after I finished this show! That makes me even more certain of his acting range, as he can have a totally different vibe. 

I also scrolled through YYL's insta and it's the complete opposite of what I expected! He seems like a super nice guy and the cat food is ;_;

Thanks for the translation! I was hungering for more SDOD after I finished it and this scratched my itch ^^

Loved this drama, thanks for translating all this for us!

Thank you so much for this article!!!! I searched high and low online for more to read about this drama and you have provided a gift to me writing this :D   Thank  you!  So many of my questions and more were answered now I can look forward to spending time dwelling on what  you wrote.  That is how much I loved this drama.

Being a non-Mandaring speaker, thanks for the translation! With your article I was able to appreciate this drama more.

thank you so much! I knew so much about how y new fave Taiwanese drama came about. more power!

Thank you so much for translating this! I have been feeling so empty since completing this drama. So, I've been searching for interviews from the cast members but a lot of them are not translated, so I am always confused. Thanks to you, I get to learn a bit more info about these amazing actors and team behind the series!

thank you so much for translating this! whenever i love a drama as much as i loved this one, I will always look up related articles and interviews to learn more about the behind the scenes & production -- thank you for all of these hidden insights into Someday or One Day, they really made my day!!

Thank you so much for this! I'm currently scared of Yan Yu Lin but you're changing my views on him lmao

I was wondering hence would like to read the erased spoiler part.