The situation is more complicated than this but Alastair Crooke brings out some key factors. There were actually two big mistakes that he mentions.
First is the mistake of overestimating finance and underestimating productive capacity. Andrei Martyanov had been writing about this for some years.
The second, which is related to the first, is the abject failure of intelligence to properly access the strength of the Russian economy. This is seldom mentioned but it is a huge factor. Alastair Crooke served in British intel so it is well aware of it.
These mistakes together constitute a blunder that is leading to disaster. The US and its allies either have not yet realized this or have backed themselves into a corner from which they cannot escape without climbing down, and that threatens bringing down their house.
The analysis is sort of a combination of Michael Hudson and Andrei Martyanov without mentioning either. It's not fully MMT-compliant but the thrust of the article is not dependent on this.
Strategic Culture Foundation (sanctioned by the US Treasury Department)The Most Egregious Mistake
Alastair Crooke | founder and director of the Conflicts Forum, and former British diplomat and senior figure in British intelligence and in European Union diplomacy