공자 앞에서 문자 쓴다
Confucius front-LOC letter[character] write
[…Like] writing in front of Confucius.
This is a proverb that expresses the ridiculousness of trying to teach a master. “…Trying to teach your grandmother to suck eggs” is the equivalent classic English language proverb, but that’s an English-language one that is so far out of date as to be incomprehensible to modern speakers.