Though both Ukraine and Russia were part of the former Soviet Union, they now fight using very different military doctrine.
When faced with unfavourable odds, Russia did not hesitate to retreat to more defensible positions.
Ukraine, on the other hand, would fight for every inch of land even at the cost of high casualty.
The problem is, in that area, there is plenty of land and Russia has more men. I don't think Ukraine Sacrificing Men for land is a good idea.
It is estimated that Ukraine had lost more than 60,000 men in the last three months counter offensive. To put it in perspective, Soviet Union lost 15,000 men in ten years during the Afghan War.
It is not sustainable.
