it is easy said than done.为什么用done

Question

如题所述

Answer 1

比较一下，其与主语之间的关系，可以确定。
可以这么理解：We say it easy. We do it.即主语应该是动作的承受者。完整的句子可以这样看：
It is easy to be said. It is hard to be done.
It is easy to be said than to be done.
由于是言谚语，所以要求很简洁。就变成了It is easy said than done.

Answer 2

这里指完成一件事。用现在分词的形式