אֵין סַכִּין מִתְחַדֶּדֶת אֶלָּא בְּיֶרֶךְ חֲבֶרְתָּהּ

ביטוי (אנגלית)

A knife is only sharpened by the blade of another knife

הגדרה (אנגלית)

A knife can only be sharpened by another knife. Figuratively: Studying together or in partnership enriches learners and sharpens the mind.

("Iron sharpens iron together (Proverbs 27) – Rabbi Chama bar Chanina said: A knife is only sharpened by the blade of another; so too, a Torah scholar is improved only by his colleague." – Bereishit Rabbah 69:2)