Morale and coordinated action of the Ukrainian army are needed for that. Remember that the Ukrainian army is rather young. They started mobilization this week. Russia has years of fighting experience, not alone from Syria. I certainly sympathize with Ukraine, but I am not convinced that they can stop the massively stronger aggressor.

Edit: Russian troops are not very efficient and morale might be questionable in some parts. But Putin does not care how many of them die. He has hundreds of thousands more.

The Ukraine does not have enough soldiers and not enough infrastructure to last that long.

That coupled with Germany, the US, Czech Republic, and NATO supplying supplies, weapons, etc into Ukraine. The longer it goes on the more likely it seems Ukraine will survive.

Unless Putin goes fully insane and wants to nuke Ukraine or something. Let’s hope Putin tops himself in a bunker before then.

Like a couple of thousands out of 145 millions?

The vast majority of the population has only access to state controlled propaganda. Even if they have learned for generations that their leaders and their media can generally not be believed, the vast majority believes that NATO is threatening Russia and they have to defend themselves.

One could say, well the former is profit from energy business and the and the latter is aid, you can't compare those. Doesn't matter. Putin can go to war only because Russia has made profits from exporting energy. And still energy exports are excluded from sanctions.

I would be glad if what is happening were enough to stop Putin. But I am far from convinced that it is enough.

Can he really? If he upsets too many important and powerful people in Russia, Putin risks being removed in a coup, or assassinated by his own military or intelligence services. If this war drags on for too long, if too many Russians die, if damage to the Russian economy becomes severe, that outcome starts to become a real risk for him.

NATO can make nuclear threats too. They are too classy to make them publicly like Putin does, but who can say they aren’t making nuclear threats and declaring red lines of their own behind closed doors?

Also, while Putin can make these threats, is he sufficiently suicidal to actually act on them? If he did, the likely end result would be both Russia and NATO reduced to smouldering wastelands. Even if he was suicidally insane enough to give the order, the Russian military might refuse to carry it out, they might turn on him instead.