a proverb meaning that even among close friends one should maintain boundaries and courtesy (similar to 'good fences make good neighbors').
親しき中に垣をせよ、とは仲が良くても礼儀を忘れてはいけないという意味だ。
The proverb '親しき中に垣をせよ' means that even if you are close, you must not forget manners.
先輩は『親しき中に垣をせよ』と言い、接し方に線引きをするよう助言した。
My senior advised me, saying '親しき中に垣をせよ', and suggested setting boundaries in relationships.