Reiterating from memory of his lectures on YouTube:
- The Russians consider some nine-odd geographic boundaries of the former union to be crucial to defense (e.g. between mountains and deserts, certain ports). Without fortifying there, a lot of the Rus land area is open and hard to defend. Interestingly, Ukraine contains only one in Crimea (which they already had) but is on the way to ones in Romania, Poland, etc.
- With the fall of the union, there was not only a baby bust but also the collapse of technical training programs. The "demographic cliff" means that not only will the army half in size but, e.g. the rail lines and electric are also in danger.
- While Ukrainian resolve and EU unity were a surprise to even the US, he also sees a leadership failing not unlike the Chinese one - authoritarian that drives out opposition too harshly also drives out the people in the room that push back on bad ideas. FSB had intelligence that overwhelmingly, UA would accept occupation?
