Because the program is constantly revising its strategies, in light of what's worked and what hasn't worked in the past.

因为程序会不断依据过去,有效无效经验修改其策略

耶鲁公开课 - 死亡课程节选

We'll talk more about this later, but it often happens that when you change your program to solve one problem you break it, and things that used to work don't work.

我们以后会更多的去讨论者一点，但是经常发生的情况是当你因为,一个问题修改你的程序的时候,你修改了程序,但原来没问题的模块。

麻省理工公开课 - 计算机科学及编程导论课程节选