We've reached a point in the drama I think we can safely say that there's clarity and the confusion is no more. A relief indeed because my greatest fear was that this plot would spiral ridiculously out of control and make no or little sense. Even while there's no explanation (and I doubt we'll ever get one) of the temporal device, the cloud has lifted on the chaos and madness of the past few weeks. Yes, we do have a serial killer and we do have clarification of why Lee Shin reached out to all those individuals very specifically.
A bunch of people resetted to change their fate and but they died anyway. A fairly reductionist way to put it. But of course there is/was always more to it than that. Lee Shin, a psychiatrist who is desperately trying to cure her daughter of some multi-syllable incurable disease has been resetting that particular year of her life. How she came upon this temporal device... we don't know... While doing so, it came to her attention that a serial killer was running loose during the course of the year so decided after several times that she was to take matters into her own hands. She finds an opening and the potential killer is disposed of unceremoniously except that it leads to other problems. On the next reset... the present timeline... she invites all the individuals who fell prey to the serial killer to join her and change their "fate". She doesn't tell them about their deaths or the serial killer... but offers a panacea to their unhappiness. Little by little, this crew gets picked off by the killer.
Once the killer is identified a lot does make sense. The show seemed to be pointing that way in previous episodes. It had to be someone close by and aware of what was taking place. So the question is asked, by saving the killer early on has Hyeon Ju opened the door to a lot more people dying. The answer to that depends on one's worldview. This is why LS answers it with a cryptic: "Is that what it is?" For HJ it feels like awfully like a case of "damned if you don't, damned if you do." This isn't really so much a survivor game in as much as it is an ethical dilemma. Do you kill one person to save 11? Or do you save 1 person you care about and let 11 people die? I think that's the question that weighed heavily on LS. She had the foreknowledge.
But of course it is far more complex than that. It isn't all on HJ. He's been presented as the quintessential likeable, simple-minded guy but he takes on too much responsibility for the evil that's being perpetrated. You can understand why LS kept mum. Because she wanted him to act freely without the burden of knowing that in the act of saving his senior, he indirectly causes a chain reaction. Now people aren't dominoes either. Nothing has to be inevitable. None of those people had to die during the designated time and place. I think that was what she believed. Even with a serial killer on the prowl, people given scraps of information and having an inherent fear of death may still be able to redirect their personal trajectory. She also believed, I think, that if she had a cop on board the reset, that there would be a possibility that the killer could be caught without having to kill him first and causing his loved ones heartache.
The confusion for me lay in the fact that there were all these disparate forces at play. The killer doing his thing, LS doing her thing, the leads doing their thing and all the now-dead players doing their thing. I wouldn't call them "agendas" in the usual sense but each party in this narrative, due to fear and a lack of trust were acting on their own which exacerbated the chaos.
Character is destiny is very much the thing that's driving this. That was always clear from the start. In every instance, LS is right in this regard. People had the opportunity to change course. But they didn't. Why was that... 1) Secrets that they were loath to share 2) Flaws in their personalities 3) Lack of trust 4) No interest in changing the status quo just outcomes. A cynic might say that people aren't really interested in changing until they're forced to. Just think of Se Rin for instance. She had the chance to leave town but her concern and obsession for the boyfriend overrode all her survival instincts. More than she was someone who invited trouble. Some of it was a lack of affection, some of it the Munchausen talking but she had some serious character flaws. As long as she was fixated with him, the danger was imminent. It wasn't about the time or the day, it's about what these people did to draw the notice of the killer.
I'm not saying that any of these people "deserved" to die. That's what the killer thinks most likely. But these individuals were prone to making poor choices and even criminal ones. There's little doubt they made a lot of noise one way or another.
Therefore avoiding death here is not purely about dodging metaphorical bullets. Death can't be avoided in most cases unless a person's moral or aspirational compass changes. In a way it is inevitable. There are also things we cling to... friendship, love, family, trust etc that are normally good things but can be worked against us.
That's an important issue too with regards to HJ and SH. I can't imagine what he's going through right now. Never in his wildest dreams I'm sure did he believe that someone so close to home was behind all these deaths. That's why his mind never went in that direction. This is why he had to have help from GH to come to this place. She's more than his partner... she's someone who provides another set of eyes and keeps him honest.