CAMP DAVID: President George W Bush waves while driving a golf cart with Brazil's President Luiz Inacio Lula da Silva in 2007 at Camp David, Maryland.
CAMP DAVID: President George W Bush waves while driving a golf cart with Brazil's President Luiz Inacio Lula da Silva in 2007 at Camp David, Maryland. - 

You know I'm a sovereign debt geek, so my number would be 2,000. That's the spread over Treasuries, in basis points, of Brazil's sovereign debt in 2002.

Which — OK! I know that's super-geeky and hard to explain. But let me try!

Back in 2002, Brazil had just elected a leftist president, Lula, and it was right next door to a bona fide basket case, Argentina. It had a lot of short-term debt maturing very soon, and no easy way to roll that debt over, since the capital markets were pretty much closed. (No one trusted Lula.) So in a self-fulfilling prophecy, the markets started pricing in a massive default on Brazilian debt.

What that meant in practice was that you could buy a Brazilian bond — any bond — and its yield would be more than 20 percentage points higher than the yield you could get on a U.S. Treasury bond with the same maturity. Not 20 percent higher, 20 percentage points higher. So if the Treasury bond was yielding 5 percent, the Brazilian bond wouldn't yield 6 percent, it would yield 25 percent.

At the time, no country had ever seen its debt trade at 2,000 basis points over Treasuries without defaulting, and it's easy to see why. At those levels, you can't refinance your debt as it comes due, which means that you have no choice but to default on it.

Except, Brazil proved the exception to the rule. Lula was fiscally conservative, and he appointed a George Soros aide, Arminio Fraga, to run the central bank. Between them, Lula and Fraga managed to muddle through the crisis and get Brazil's debt back onto a sustainable footing. And anybody who bought Brazilian debt in the summer of 2002 ended up making an absolute fortune. (The person who bought the most, and who made the biggest profits? Mohamed El-Erian, then of Pimco, later of Harvard, and later still of Pimco, again.)

I learned a huge amount from this episode. Firstly, and most importantly, just because something has never happened before, doesn't mean it's impossible. Secondly, sovereign debt can be even more volatile and risky than stocks — and provide even bigger profits. Thirdly, policymakers can make an enormous difference. And fourthly, markets aren't always rational, or correct: there's a wisdom of crowds, to be sure, but it has its limits.

So the next time you see a country's debt trading at 2,000 basis points over Treasuries, and you hear me saying that default is inevitable, remind me that I said exactly the same thing back in 2002. And I was wrong then.

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Follow Felix Salmon at @felixsalmon