Thinking about Viktor, knowing that he is going to die and convinced there is no way to save himself (refusing to use the Hexcore as a potential out) watching Jayce give himself false hope about his survival.
He watches Jayce run himself ragged between the Council and the lab, attempting to both stick his hand in Piltover's core while also pursuing research on Viktor's behalf. He probably watched Jayce lose sleep over it, watched him pull away from other people for it (c'mon now, we all know Jayce likely didn't have time for much like his mom or Caitlyn during that period), all while being convinced their 'life-saving research' will go somewhere.
Viktor gets to witness all of it, and he stays quiet, because what else can he do? He wants to live too. He's known that his disease would likely take at least half his life off the block, but he *wants* to live, damn it. He wants to pretend that Jayce's efforts will actually go anywhere.
And maybe he does have some kind of hope for it. At first, at least, the hexcore is actually working. Shimmer is working. Until it kills Sky, and he can no longer support his own survival if it means the potential to hurt or kill another person (let alone someone he adored as much as Sky).
I can imagine him contemplating his suicide attempt. I don't think it was as much spontaneous as Jayce's was (sure, it could've been a part of it) but it seemed planned in advance. He chose a secluded spot, overlooking Zaun, from what I remember, in a place that no one would likely find him for some time. Viktor was hesitant because he knew this was coming, unlike Jayce that fully embraced the idea of killing himself on a whim to avoid his life falling apart.
I can, also, imagine his realization that he cannot die on his own terms. Because Jayce is here, because he knows Jayce *needs* him here.
But he also can't keep letting Jayce chase the false hope they both had, because it'll only make his death worse. He can't let Jayce try something he knows he will, because it'll only end up hurting someone. It already killed Sky.
So he tells Jayce to break the Hexcore, not only because Viktor is terrified of what its capable of and hates what its done, but because he can't let Jayce think it isn't over. He needs Jayce to start processing the inevitable while Viktor is still alive.
He cannot die knowing it will break Jayce in two. The most he can do, unfortunately, is try and prepare him for what's coming.













