That is it's dictionary definition, that you keep going because you invested too much. Whether you have resources to continue to pour in is irrelevant, that's why the Americans and at the time Global Colonial Powers who had comparatively far more resources than Putin's Russia, could still engage in quagmires.
I think you didn't get my point about sunk costs. The explanation is simply that Russia can't pick their bags up and leave, because it would be political suicide. Whether the decision would be rational or not is up for debate. It's impossible to predict accurately simply because we don't have the information. The Russians should know a thing or two about quagmires, they were kicked out of Afghanistan as well.
That was before we actually interacted with each other for this segment.
The OUN operated even before WW2 started. And there is an Ukrainian ultranationalist movement that reveres people like Stepan Bandera. You can see portraits of the guy in the offices of Ukrainian politicians and generals. Russians bring it up for propaganda all the time, but the questionable history behind the movement is completely real. I mentioned Iryna Farion as well. Read the Wikipedia article on her. I don't think it's a reach to think the Russians would want to suppress that movement. Whether you think it's justifiable or not is beside the point.
Let's make a trade. You answer in detail first what casus belli Russia has on Ukraine, other than the sunk cost fallacy. I've had glimpses of it, but I want to know clearly who I'm debating. Than I'll answer.
If you mean geopolitically, it's most likely about control of Crimea and the Black Sea being threatened. What territory was annexed by Russia in 2014? It's no secret that Ukraine has been very focused on trying to push Russia out, the entire 2023 counteroffensive being about cutting through the defenses into Mariupol, destroy the Kerch bridge and isolate the peninsula.
It's also worth noting that the one thing both sides are adamant on is Ukraine's NATO membership. You may think it's about Article 5 and Ukraine not being invaded in the future, but why did Russia not make a fuss about Finland joining NATO? I think it's more about the US Navy having a permanent base on Sevastopol. Putin betting on ousting the Ukraine government and placing one that constitutionally guaranteed no NATO membership, thus no risk of retaking Crimea, sounds to me like the most logical reason for the invasion. Which again, the legality or morality are completely beside the point. I'm not bringing it up to justify it, if that's why you're implying.
… Do the lives of the Russians lost in their advance not mean anything to you?
They do. Which is why I'm wondering what would be the point at which the war should be stopped. I just see it much more likely that Ukraine will be the one forced to take the decision, not Russia.
They're advancing at the rate of WWI. To use your own argument, how much would it take to even attempt to take Kyiv again? Kherson? How much to actually take instead them of just destroying like Bakhmut? How much to hold it, how much to guard it considering you mentioned regime change and it may be like Belarus? How many manpower reserves until the actual muscovites? You mentioned the impossibility of the task, do the Russians actually have a pathway to anything?
That is actually a very good question. DeepState doesn't mark Ukrainian defenses, but from other mappers I've seen, the Ukrainian defenses get less dense the further west you go, because Ukraine had been digging trenches and fortifications in the Donbas as far back as 2014. Thing is, instead of maneuver warfare, Russia is using attrition war tactics, because the terrain, fortifications and technology don't allow for any big maneuvers. That's the big difference between something like Kursk and the Donbas. In attrition war you keep your forces within defensive artillery range, bomb the hell out of everything first and then advance slowly and methodically, first with small unit tactics to secure footholds, then bring in more troops, with many shallow advances across the front rather than one big push. And the goal is to slowly degrade the combat capability of the enemy. When one side gets enough manpower and material advantage, the lines can start to be broken through, because the enemy can no longer defend them. The side with more manpower reserves and a stronger industrial base, as well as the willingness to sacrifice them, always has the advantage. See where this is going?
You did make the claim first, something very vague about national fervour that would inflame the Russians as it has with Ukraine. Why should I define the extent of your claim? Whatever the case, I think normally that would mean an increase in conscription, partisan attacks, something in interviews than the usual "I don’t know, I don’t care, I don’t follow it”.
I said there was a possibility, because an attack from a perceived foreign enemy has a tendency of uniting people against it. Imagine if during the Iraq War, a fairly unpopular war in the US, Saddam had launched missiles into US territory. Wouldn't that be enough to turn some moderates and detractors into supporting the war? This is also why the Russians have played up the historical memory of the Battle of Kursk, "Once again enemy tanks are rolling into Kursk, foreign invaders are attacking for the first time since WWII". Whether that is working or not, I cannot say. I do not live in Russia and I don't particularly care for interviews that can be easily cherrypicked by media supporting either side.
Seems Kursk has been left to rot by Moscow, considering attempts to present it as a new normal
Because, strategically, they don't have a reason to stop it. By nature, offensive operations tend to have a higher cost than defensive ones. In manpower, fuel, ammunition and casualties. The further you advance, the further you need to stretch your supply lines, the more difficult it is to rotate troops and evacuate casualties. For the attacker it is important to keep advancing, for example, in order to secure new logistic hubs, but ultimately there has to be an strategic goal in mind. As in Pokrovsk, where the goal is to remove the logistic hub for Slovianksk, Kramatorsk and most of the southeast of Donbas.
In Kursk there is no such logical strategic goal. If the Ukrainian goal was to lure Russian forces away from the Donbas, and the Russians instead keep the Ukrainian forces tied up in Kursk with the bare minimum of reserves, while they keep the momentum elsewhere, it would not make sense to change the strategy, no matter how bad it may look to the public in Russia to have Ukrainians roaming around Kursk, or how disastrous it is for the displaced civilians.
Would the resources have been better used for Pokrovsk? We'll have to see, maybe I'll eat my words but fog of war is in full-effect, as you said:
"Anything said would be based purely on wishful thinking"
Not wishful thinking, it's basic military logic. The 47th Mechanized Brigade was achieving some pretty good results in the southeast with their Western equipment and tactics. For example, the Russians would storm a location and the 47th would attempt to flank them and inflict casualties before retreating. Now they've been redeployed into Kursk where they're taking casualties from Lancets and drones, for what is to me still an unclear purpose, while the Russians keep advancing elsewhere. Maybe they're making some sort of brilliant 4D chess play I'm way too dumb to understand, but I guess time will tell.