You came on our land and you start to kill our people. We are going to eliminate this threat whatever is the cost. You still have a little chance to make few steps back and survive. But, I'm almost sure, you are too stupid to use it.
But we are already in the initial phase of WWIII, and, pretty likely, future historians will call the current situation on the Ukrainain front - "phoney war". Its almost nothing comparing with WWII, WWI, Napoleon war, Sweden invasion, Lithuanian wars, Time of Troubles and other similar conflicts.