Oftentimes the debacle on Wall Street is painted as too complex even for the executives involved to understand. Merrill’s near collapse was easy to understand, though. They bought mortgages that nobody else wanted and repackaged them into securities that they couldn’t sell. They had a couple of huge warning flags. AIG stopped insuring these securities against default in 2005; when one of the world’s largest insurance companies says that these things are too risky for it to insure at any price, you’d think that anyone holding $32 billion of such items would take notice.