that has a capital requirement,

任何资本充足率良好的金融机构
when they lose money,

当他们赔钱时都会收到
there is a margin call or a need to generate capital,

一份追加保证金通知或者直接补仓
which can lead to the liquidation--that can lead to the liquidation of positions.

否则将会被强行平仓这将导致被平仓
Again, falling price, more selling.

再说一遍薄利多销
A fifth example and a fifth source of positive feedback

第五个例子即第五种能产生正反馈的来源
comes from what one might think of as model uncertainty.

来自于人们可能会想到的模型不确定性
There are different ways to tell the story

有多种表述方式
and I suspect it could be given much more rigorous formalization

我猜还有很多比我在这儿说的
than I'm going to attempt here.

更严密的形式
A prominent macroeconomist, early in his career,

有位杰出的宏观经济学家在他事业早期
developed on the basis of some macroeconomic model

基于一些他有坚定看法的宏观经济模型