知古不知今,谓之陆沉,然则儒生,所谓陆沉者也。
解释:了解古代不了解现在,称为愚昧无知,那么儒生就只能称作愚昧无知的人了。
A good abstraction is one that captures the essential aspects of a concept while ignoring the irrelevant details.
Courage is what it takes to stand up and speak; courage is also what it takes to sit down and listen.