I don't think he is correct. Debt can be sustained as long as there are marginal returns to be had. The real problem is that the marginal returns are no longer there because energy prices have been increasing at the same pace. This suggests that energy availability to be the limiting factor.

Once growth is throttled by expensive energy, the debt position of countries, companies and individuals start to look shaky. This is what is happening now. If companies are unable to increase their profitability, then there is less taxes to be collected, which means weaker governments, and a slower economy. This in turn affects an individual's ability to find and keep work, and service their debts.