one would expect them to know their parts by heart and never have cause to falter.yet this is not al

题目

one would expect them to know their parts by heart and never have cause to falter.yet this is not always the case.
这句话里的one would expect them to know their parts by heart里面有固定搭配吗 by heart是什么用法
还有yet this is not always the case该怎么理解呢 因为我按照这句话的意思翻译出来觉得有点奇怪

答案

expect sb.to do sth.
期待某人做某事
by heart的意思是“用心地”
yet this is not always the case
表示“但是,情况并非总是如此”
翻译：我们总是期望他们用心地记住他们自己的工作并且不会停下来去犹豫.但是,情况并非总是如此.