I don't get up and go to work because working brings my heart pure joy. I go to work because I get paid, and then I can go to shop and buy some shit like food or something. When I lose the job, I don't buy shit. When enough people lose their jobs, people doesn't buy wares, enterprises goes bankrupt. Enterprises going bankrupt, mean that they stop producing all the things people want to buy. Like soldiers, who would like to have something more in life than bread and vodka. At some point of crisis, it is not only difficult to support soldiers with their "wants", but also with their "needs". All of which impacts their effectiveness and possibilities of continuing operations.
Add to that internal disapproval. Predicted inflation is 20%, predicted gdp drop is 10%, so roughly average russian will consume 1/3 less that before war. Do you think that they will be able to push that all on "the rotten west"? At some point people are angry, no matter if Putin tells them that's because of USA or not. You will need extra forces to keep peace internally. Wich turns into additional expenses.
All this expenses are rising and rising, toghether with regular war expenses. What about incomes and savings? 460 miliards USD out of 600 miliards has been frozen. Now it is spring, so Europe uses less natural gas. In all EU, including germany there are opening possibilities of importing gas through other channels like from Katar. By winter 2022 Europe as a whole will import much less gas. Moreover many, many of Russian oil loads can't have a buyer because of blockade.
At some point, gears will stop spinning.