find it中的it是形式宾语， it代替不定式短语。 构成句型:think/ find/ feel/ consider/ make/ regard…+ it +形容词/名词 + 不定式短语，例如如：I find it pleasant to work with him. 其中it 作形式宾语，代替不定式短语to work with him。句子的意思为:我觉得和他一起工作很愉快。

②They felt it difficult to finish the work in such a short time.

it值得是句子前面指的东西