Russian soldiers were lied to about going to Ukraine. They use contract soldiers, and under Russian law if they want to get out of Ukraine to go back to Russia, they have to write a letter to their CO about it. The Russian "stop loss" program is to ignore Russian law and not act on any of the letters. The soldiers not trying to get out, can take a guess at what's going on with those who are. I can't confirm the number, but its supposedly sizable, maybe 30-40%.
Then there is the leadership, HIMARs attacks for two months, and the emphasis on Battalion sized units for organization making command and logistics harder. Prior to the Kherson action, Russia relocated force to Izyum and Kherson. The forces in Kharkiv are large the Donbas and Luhansk militias, second rate Russian proxy forces, and Wagner group mercenaries who are not allowed to engage in offensive operations by law or they don't get paid (supposedly), and want to live to get paid more than die Putin's ambitions.
After HIMARs started fighting in July, Russian advances slowed to a halt. What they gained in Donbas, Ukraine could afford to lose. What HIMARs was destroying was gradually wearing away at the Russian ability to wage war.
A week into the Kherson counter offensive, the Kharkiv conter offenses starts. Two days later Ukrainian forces are rasing flags 30 miles behind Russian lies. 10 to 20 thousand are back up to a river with the Ukrainian army everywhere else. 20,000 are stuck in Kherson because HIMARS took out bridges and where there aren't bridges there's the Ukrainian army. 30,000 to 40,000 Russian forces are backed up aganist a wall, imobilized, with command and control that is
In three months time, Ukraine found a way to get inside the Russia OODA look like no one has since World War II.
The only wonder is why people believe it is impossible for the Russian army to be routed like this, a week after the fact.
All of this and with winter just two months away.