It is that we can't always know. When we know of an impending disaster, and how to solve it at a cost less than the cost of the disaster itself, then there's not going to be much argument, really.
事实是我们不可能永远知道。当我们知道有一个灾难将要降临， 应对这个灾难的成本要比灾难本身小， 那么就真的没有什么好争论的。