Because nobody - no Ukraine, no Russia: really nobody - can hold the entire frontline occupied with…

In this case, the point is this: the Russians have critically reduced their forces everywhere else to a bare minimum - though they have…

Because nobody - no Ukraine, no Russia: really nobody - can hold the entire frontline occupied with equally strong forces. That's physically impossible.

In this case, the point is this: the Russians have critically reduced their forces everywhere else to a bare minimum - though they have reduced Ukrainian forces along the LOC to a minimum, too (i.e. made them unable of doing more than defending).

Ukrainians were then much too cautious and, obviously for political reasons (Kharkiv is the second largest city in Ukraine) counterattacked 'in wrong place'.

....which is a place the Keystone Cops can't care less about. Instead, the Russians then concentrated on two points: Lyman-Ozerne and Popasna-Avdiivka. The Ukrainians didn't. And that's now a problem - because the Russians have enough troops between Lyman and Popasna to close the gap.