Adam Clarke on Ecclesiastes 10:2

A wise man's heart is at his right hand - As the right hand is ordinarily the best exercised, strongest, and most ready, and the left the contrary, they show,

1. The command which the wise man has over his own mind, feelings, passions, etc., and the prudence with which he acts. And,

2. The want of prudence and management in the fool, who has no restraint on his passions, and no rule or guard upon his tongue. The right hand and the left are used in Scripture to express good and evil. The wise man is always employed in doing good; the fool, in nonsense or evil.