Iron whets iron.
More Biblical Proverbs:
The prosperity of fools shall destroy them.Biblical
Every wise woman builds her house: but the fool plucks it down with her hands.
Biblical
Great men are not always wise.
Biblical
A prudent wife is from the Lord.
Biblical
The rebellious dwell in a dry land.
Biblical
Faithful are the wounds of a friend; but the kisses of an enemy are deceitful.
Biblical