Proverbs 17:18

A man void of understanding striketh hands,.... With his friend's creditor, and becomes surety for him; and thereby acts a very unwise part, and shows himself to want understanding, by taking such a step, which may prove the ruin of himself and family: for though a man may and should love his friend at all times; yet he is not obliged, under a notion of friendship, to injure himself and his family, or to run the risk of it; if he does, it is a plain case he wants wisdom and discretion, see Proverbs 6:1;

[and] becometh surety in the presence of his friend; not the creditor, but the debtor; and to pass his word for him, when he is present, shows that his own word will not be taken; and that he is either thought to be in bad circumstances, and incapable of payment at the proper time; or else that he is a bad man, of dishonest principles, and will not; and in either case it is not advisable to become surety for such a man: and besides, doing it in his presence may make him more careless and unconcerned about making good his payment or contract at the appointed time, when he knows his friend is engaged him.