In the case of Bear Stearns, as house prices fell and mortgage defaults increased, the value of its investments fell, and its "collateral calls" (what the people it borrowed from would accept to continue lending to the company) rose. As a consequence, Bear Stearns' reputation fell and so did its capacity to borrow, which was a disaster given how much it was levered-up (how much debt it carried relative to its assets).

Mark Blyth, Austerity, loc. 83