Your debt and the government's debt. Why are they different?

There are some concepts that, even though they've been in circulation for many years, are still hard for most of us to wrap our minds around. Like Einstein's theory of relativity. Or how global warming makes winter storms. Or, especially recently, government debt. 

What's so strange about debt?

First there's debt that's intuitive. Most of us would probably say debt is OK when it allows us to do something that's long-term beneficial that we couldn't otherwise do. Like buy a car or a house. 

But when things get financially tough we all feel we should hold as little debt as possible. That's sound strategy for a person or a family. Even a city.

But countries are different. Just as how, in the theory of relativity, the normal rules of life break down when we approach light speed, so it is with money when you approach the  size of a country. At that large a scale, when things get financially tough, it's actually in the country's best interest to take on more debt, not less. 

Paul Krugman does a good job explaining why in a short article that contains no numbers and no graphs and very few wonky words,  Full disclosure: I studied economics and physics and I understood the theory of relativity (kind of) even before I understood the theory of government debt. I wish I had Krugman as a professor!