A man void of understanding striketh hands, and becometh surety in the presence of his friend.
– Proverbs 17:18
The word for surety means a security, or guaranty. The phrase striketh hands refers to entering into an obligation to pay the debt of another, hence putting up the security, or collateral. The phrase void of understanding could be put more homely as, without a brain. Solomon touched on this in one of his addresses in Proverbs 6:1-5. It is generally portrayed as foolish in Proverbs to become surety and usually comes with negative consequences (Proverbs 11:15).