The Northern Rock fallacy

The Bear failed for exactly the same reason as Northern Rock it seems. From the FT, reporting Christopher Cox's testimony to the Senate:

Mr Cox said Bear had been hit by an unprecedented situation in which it had been unable to access liquidity. He said that “what [no] … existing regulatory model has taken into account is the possibility that secured funding, even that backed by high-quality collateral such as US Treasury and agency securities, could become unavailable. The existing models for both commercial and investment banks are premised on the expectancy that secured funding, albeit perhaps on less favourable terms than normal, would be available in any market environment.”

Now I can understand Northern Rock thinking that the secured and interbank markets would not shut to them at the same time. But what I can't understand is why, having seen what happened to the Crock, the Bear thought it could not happen to them.