The article discusses how countries can default on their debts when they can't pay back what they owe. The researchers use a model to show that there is a specific point where default becomes likely. They also define two thresholds for debt sustainability: one where the debt can be paid off without defaulting, and one where default is inevitable. If a country's debt falls in between these thresholds, it's in a risky financial situation. The study also shows that even if a country recovers some money after defaulting, it may still struggle to manage its debt in the future.