as a old saying goes,don't judge a book by its cover.

问题描述:

as a old saying goes,don't judge a book by its cover.
这里为什么用goes,goes是什么意识?
为什么用goes,而不用tells,says,

这是习惯说法,应该是
俗话说,不要以貌取人的意思
个人见解