“Don’t Teach Your Grandmother to Suck Eggs” in Japanese 

“Don’t teach your grandmother to suck eggs” is an idiom that means you should not try to teach someone who is more experienced or knowledgeable than you about a subject. It implies that the person you are trying to teach already knows more than you do and that you would be wasting your time.

Preaching to Buddha

There is a Japanese idiom that has the same meaning as “Don’t teach your grandmother to suck eggs,” which is 釈迦に説法 /ʃjaka ni seppou/.

釈迦に説法 is a proverb that means it is pointless to preach to someone who is more knowledgeable and experienced than oneself, especially if they are a famous person.

釈迦 /ʃjaka/ refers to Siddhartha Gautama, also known as the first Buddha in Buddhism. 説法 /seppou/ means preaching. Thus, the idiom translates to “preaching to Buddha” in a literal sense.