First question, whose experiment? There was like 3.
In this case, Florencia's. The medals collecting was her thing, and is what opens that path.
I guess what bothers me most is if just not going to the mansion at all solves everything, why Roswell didn't call it off before? Besides that, I'd like a explicit explanation how this version of the events, makes using the medicine a viable option. Berek07's conjecture is good, but I was hoping that the story would have told me that.
Florencia's experiment was to save her brother and her son. Roswell was terminal with no prospects outside obsessing over a rat that had seen how things play out, and Oswin had given up hope living after his experiment and had to watch his son call someone else dad.
The reason Roswell didn't call it off before is because not going to the mansion doesn't solve the problem. He's tried, it's why we see glimpses of a timeline where Dave is a sole survivor, so that was a no-go. I think an important thing to remember is that Roswell's goal was to keep Dave alive, Thanatos's goal was to keep Roswell alive as much as he could, even in the face of Roswell's wants, and then Florencia just wanted her family fixed.
So why the medals? Because they're impossible to get in one run. They could've been anything at all, just a set of objects that she could've hidden in the same way. It would've required Dave to experience/remember the fact he's looped even with Thanatos as a witness.
The normal question now is usually "So does the medicine work or doesn't it?" the answer is "We don't know." It's a quantum mechanics thing referred to as a wave function collapse, though most people recognize the concept as Schrodinger's cat. All the possibilities of how this medicine works, if it works, is now consolidated into one outcome: which we know due to outside sources that yes, it will work.
As far as providing this explicitly in game, it becomes hard to treat readers with respect for their intelligence with things like this when the alternative is to just open a Wikipedia page on the subject and deliver it up-front. I could have Florencia or someone monologue for a while to get it all down, but at what point does it just become a clunky mess when in-universe Dave isn't going to understand anyway.
It didn't have to be a long winded explanation from her. Florencia could have been like, "Oh so it's actually happening. See, I told you Oz that as long as you try, the impossible could work. This right here is proof of it." and then Oswin, "You know what, you are right. But I'll let Roswell to choose if he wants to risk it or not". Dave doesn't need to understand that interaction.
I still find value in you explaining further, if only because these are the kinds of things that inform how I need to edit this beast into something more refined.
EDIT: I think using the message "keep trying and you'll achieve the impossible" isn't exactly on the money either. So using your example wholesale wouldn't work.
Well, the idea here is showing how Dave remembering things convinces Oswin to try. That's the main connection missing, and that's precisely what makes it difficult to point out what it is. There are a number of options to how that could play. Maybe it was due to Florencia proving her point. Maybe it was just the sheer absurdity of the experiment working at all. Or it could also be something that Dave lets slip out when talking about the approaching events. How the vacation is going to be a bad idea, and realizing Roswell is in dire need of a course correction, possibly in the form of that medicine being made available to him. The other thing would be showing why calling the vacation off works this time, but my guess is that Dave's inherited memories effectively makes him a different person than he would have been at this point in such a way that the potential dangers never arises. These are the 2 selling points that explain why the true end works out. The medicine effectiveness isn't as important.
Still, I don't want to be nagging so much on these details. They don't detract at all from the rest of the story, which is really fun.
Oh, it's not nagging at all. At least I'm not seeing it as such.
The question I would pose is "Oswin is being convinced to try what?" because that's something maybe I'm not understanding. Florencia is the one who's like "Oh how interesting, let's fuck around and find out" and throwing caution to the wind. Even though Oswin is being compelled towards accessing the elixir, he's not actively trying to use it. He's just making it available for Roswell to choose.
Well, that goes to show how this scene has confused me. Without her experiment, the medicine is just left sitting there. The risk of it being lethal remains true in both scenarios, which is reasonable motive to hide it in the first place. So what has changed that opens this option for Roswell in spite of the danger?
Well, for Roswell it's easy. Dave remembering the vacation means he won't be able to follow with his plans. So it forces him to reevaluate things. Oswin is the one that i just can't find the reasoning. My best guess is seeing Roswell distraught might make him more willing to present the option of the medicine. It's a stretch but i can't come up with something better.
If calling off the mansion doesn't stop people from dying is there any reason not to believe that someone/everyone is likely to die at the beach vacation in the true end?
Edit: Nevermind, read the other comment about how Thanatos dying counts as "the death" that is required for fate to by filled. Guess that makes sense enough now.