" Goldman Sachs itself—and so Goldman was in the position of selling bonds to its customers created by its own traders, so they might bet against them. Secondly, there was a crude, messy, slow, but acceptable substitute for Mike Burry’s credit default swaps: the actual cash bonds. According to a former Goldman derivatives trader, Goldman would buy the triple-A tranche of some CDO, pair it off with the credit default swaps AIG sold Goldman that insured the tranche (at a cost well below the yield on the tranche), declare the entire package risk-free, and hold it off its balance sheet. Of course, the whole thing wasn’t risk-free: If AIG went bust, the insurance was worthless, and Goldman could lose everything. Today Goldman Sachs is, to put it mildly, unhelpful when asked to explain exactly what it did, and this lack of transparency extends to its own shareholders. “If a team of forensic accountants went over Goldman’s books, they’d be shocked at just how good Goldman is at hiding things, "

― Michael Lewis , The Big Short: Inside the Doomsday Machine