Matthew Henry on Proverbs 30:15-17

Cruelty and covetousness are two daughters of the horseleech, that still cry, “Give, give,” and they are continually uneasy to themselves. Four things never are satisfied, to which these devourers are compared. Those are never rich that are always coveting. And many who have come to a bad end, have owned that their wicked courses began by despising their parents' authority.