èr rén tóng xīn, qí lì duàn jīn 二人同心，其利断金
If Two People Are of the Same Mind, Their Combined Strength Can Break Metal.
When two people are of the same mind, their combined strength is like a sharp blade which can cut through metal. “Two people” here could mean two brothers, husband and wife, or any two persons working together. “Of the same mind” here means the people sharing the same vision and thinking. This metaphorical term means that people of the same mind will create great strength and can overcome any obstacles. It stresses the importance of concerted efforts and cooperation, which will generate great power.
If two people are of the same mind, their combined strength can cut through a piece of metal. Words of people with the same mind smell as fragrant as orchids. (The Book of Changes)