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?
Roswell isn't in control anymore. Dave remembers, so everything Roswell had been tunnel visioned over, everything that he'd 'decided' was now incorrect.
This is why I feel that there's no good way of explaining this without having a mini-lecture on quantum mechanics in-game. Roswell observed reality as him being doomed to die, so it was true. Oswin observed his medicine was a failure and that saving his son was out of reach, so it was true. Florencia as an agent of chaos decided to test this and thus didn't observe anything beyond seeing her family needing saving from themselves but within herself was incapable. Dave recalling the events of the game observed an option and existed as a contradition to Roswell's observation. If Roswell was observing reality one way but concrete proof in front of him directly contradicted it, his reality flips to the inverse: He's not doomed to die. In the same way, Oswin's observation in light of this is the same, flipping to 'his son can be saved, his medicine wasn't a failure.
Florencia, who understands quantum mechanics, decides to open the door witnessing the way the universe is now being observed and thus opens the vault in the same way we open the box and see if the cat is alive or dead.
Ok, so Dave remembering Roswell's many failures offers a new perspective that prevents the disasters to come. That part is the easy one. How that also subverts Oswin's perspective of the medicine being a failure, still eludes me. Honestly, i find it would have been easier for Roswell to interject in that scene, now with the the broken paradigm, to express he wishes to try the medicine later on. It wouldn't be weird for Oswin to go along with it seeing as he is pretty lenient with Roswell in general.
To do that within the scene wouldn't be appropriate with Roswell grieving over losing Thanatos though. While in supplementary material Oswin is lenient and lets it be Roswell's choice, there isn't room for it in that scene and by the time we've moved on, Roswell isn't present to deliver in dialogue what he wants.