IIUC, one reason we're in this mess is that nobody has any idea what the securities at the bottom of this house of cards are really worth; the risk models that

IIUC, one reason we're in this mess is that nobody has any idea what the securities at the bottom of this house of cards are really worth; the risk models that were constructed during the inflation of the bubble have been discredited but nobody knows what to replace them with. So private banks weren't willing to hang $85B of their own capital out on the hope that they didn't get any more surprises. The Fed doesn't know what those securities are worth, either, but they can calculate what preventing a collapse of the financial system is worth, and compared to that, $85B is chump change.