Yay! Today is sub-prime mortgage day on kottke.org, I guess. The collapse of the sub-prime mortgage market took everyone on Wall Street by surprise…except Goldman Sachs, which earned $11.6 billion in 2007 when everyone else lost money. How’d they do it? Michael Lewis says that Goldman went against the flow in shorting sub-prime mortgages by assuming that the entire rest of the industry, including their own expert and extremely well-paid traders, were, as Lewis puts it, “a bunch of idiots”.