I would suggest nobody has any idea just what the fuck is going to happen.
Let's step back to 1914. The assassination of Franz Ferdinand and his wife was an international incident that ended up dragging just about all of Europe, Russia, Japan, and later the USA into a world war. Maybe the slide down that slippery slope could have been halted by cooler heads, maybe not. But millions of people died.
Like it or not, suggest some similarities and some differences. Here, neither Ukraine nor Russia are members of any treaty organizations or have mutual-aid treaties, unlike Germany and Austro-Hungary, and Great Britain and France. The challenge is to keep the war confined to Russia and Ukraine. This is hard and will only become more and more difficult as the Russians continue their attacks into Ukraine and capture certain cities.
The hard fact is Ukraine isn't a NATO member. Don't even think Ukraine has been designated an "major non-NATO ally", like Afghanistan was. Seriously. Hillary herself made that declaration when she was SecState. Almost puked when I heard it.
All of us have things about which we don't act or react rationally. Sometimes these things can be small, such as foods or clothes, sometimes kids. Suggest Putin isn't acting or reacting all that rationally about Ukraine. He wants that buffer state, and he wants to punish Ukraine for their sheer nerve in acting like a sovereign, independent state, and nothing else will do. Not the actions of a rational person; a weakness has been exposed. Our problem is Putin has a large nuclear arsenal. You like to think Putin wouldn't use nukes, but we also liked to think he wouldn't invade Ukraine. Russia simply cannot fight and win a conventional WWIII. So NATO stays behind the Polish border, providing support, and making sure this doesn't turn into a Third World War.