Congratulations to Brian Romanchuk for taking the p*ss out of the word “sustainable”. The title of his article is “Fiscal Sustainability And The Fiscal Folk Theorem”.
You can always spot the brain dead by their parrot like repetition of fashionable words and phrases. There are numerous such words and phrases, e.g.: “Sieg Heil”, “Allahu Akbar”, “Black Lives Matter”, “Strong and stable”, and of course “sustainable”.
Granted there are some forms of sustainability that are clearly desirable. For example mankind's economic activities must be environmentally sustainable: i.e. not lead to excessive global warming.
But the word sustainable is often used in circumstances where the “sustainable” concept is irrelevant. A classic example is the fiscal sustainability, as explained by Brian Romanchuk.
The fact that a fiscal deficit is not sustainable in the long run is not, repeat not an argument against running such a deficit for a limited period. By way of analogy, an accelerating car is not a sustainable system because the car will at some point reach its maximum possible speed, or the maximum legal speed on the stretch of road it happens to be on. That is not an argument for making car accelerator pedals illegal! I.e. it is useful to be able to accelerate a car from zero to fifty miles an hour, as you may possibly have discovered with your own car…:-)