There are two sorts of countries: countries that can print money to pay their sovereign debts; and countries that can't. Canada is a printer; Greece is a non-printer.
Both sorts of countries can get into trouble if they issue too much sovereign debt; but they get into very different types of trouble. Printers get into negative feedback trouble; non-printers get into positive feedback trouble. Positive feedback is always worse than negative feedback, when a bad thing happens. (And positive feedback is always better than negative feedback, when a good thing happens).
Positive feedback is a circular feedback loop that tends to amplify the effects of an initial shock. If the positive feedback gain exceeds one, the second round is bigger than the initial shock, the third round is bigger still, and the total effect gets bigger and bigger until the system explodes. If the positive feedback gain is less than one, the second round is smaller than the initial shock, and the third round is smaller still, and the total effect, while bigger than the original shock, is still finite. The Keynesian multiplier is a positive feedback loop. If the marginal propensity to consume is less than one, the multiplier is greater than one but finite.
Negative feedback is a circular feedback loop that tends to diminish the effects of the initial shock. The second round goes in the opposite direction of the initial shock, and so offsets its effects to a greater or lesser extent. A household thermostat is a negative feedback loop.
Suppose a country issues too much sovereign debt and gets into trouble. Nobody wants to buy any more of its debt, and it has to pay back the existing debt when it comes due.
If the country is a printer, it can print money to pay its debt. If it's in recession, and risks deflation, that's not a problem. Printing money increases demand, which is what you want if you are in a recession. Printing money causes inflation, which is also what you want if you risk deflation. Deflation + inflation = stable prices.
If it prints money and is not in a recession, or has inflation, then that is a problem. Printing money will make inflation worse, and that's a problem. But it's a negative feedback problem. The inflation will lower the real value of the existing debt, making it easier to pay off.
That doesn't mean it's not a problem. The country can't keep borrowing, printing, and inflating forever, because nominal interest rates will rise with expected inflation. There is a limit to how much real revenue you can get by printing money permanently.
You can pay off your debt by printing money, but maybe only once. If lenders expect you to do it again, they won't lend to you. Your reputation suffers, which will make it harder to borrow in future. And you might need to borrow in future. It's not painless.
But if the country in trouble is a non-printer, it's worse. It has to raise taxes or cut government spending to pay the debt. But that tightening of fiscal policy will cause a fall in demand, which may cause a recession and deflation. The recession reduces the country's income and tax revenues, which makes it harder to pay the debt. The deflation increases the real value of the debt, which also makes it harder to pay. So the country will need to raise taxes or cut government spending still further. This is the positive feedback loop. It makes a bad situation worse. If the positive feedback gain exceeds one, the country will have to default, however much it tries. Edward Hugh calls this the debt snowball problem.
Default isn't any better than inflation for your reputation as a borrower.
Debt for a printer is a bit like equity. If things go bad for a country, and it has to print, both the country and the lender share the pain.
Debt for a non-printer is, well, just like debt. If things go bad for the country, it bears all the pain, and then some, because of the positive feedback effects.