Because it says, your program will still give you a value, but it may not be what you intended, and you can't always tell, and that may propagate it's way down through a whole bunch of other computations before it causes some catastrophic failure.

因为这意味着，你的程序依然会返回一个值，但是这个值可能不是你想要的，你可能还分辨不出来，而且这种情况会传播,结果会沿着正果计算过程传播下去,直到产生一个灾难性的错误。

麻省理工公开课 - 计算机科学及编程导论课程节选