老师好，请老师帮忙看下我分析的是否正确，谢谢！

If they knew  how difficult it was to drill through the hard rock , they would lose heart.

从句是由if引导的与现在事实不符的非真实条件状语从句，在这个从句中包含了一个宾语从句（how difficult it was to drill through the hard rock），在这个宾语从句中，it为形式主语，真正主语为to drill through the hard rock。

期待老师回复！