The beauty of the credit default swap, or CDS, was that it solved the timing problem. Eisman no longer needed to guess exactly when the subprime mortgage market would crash. It also allowed him to make the bet without laying down cash up front, and put him in a position to win many times the sums he could possibly lose. Worst case: Insolvent Americans somehow paid off their subprime mortgage loans, and you were stuck paying an insurance premium of roughly 2 percent a year for as long as six years--the longest expected life span of the putatively thirty-year loans