C. F. Keil and Franz Delitzsch on Proverbs 21:23

Pro 21:23 23 He that guardeth his mouth and his tongue,      Keepeth his soul from troubles.

Pro 13:3 resembles this. He guardeth his mouth who does not speak when he does better to be silent; and he guardeth his tongue who says no more than is right and fitting. The troubles comprehend both external and internal evils, hurtful incidents and (נפשׁ) צרות לבב, Psa 25:17; Psa 31:8, i.e., distress of conscience, self-accusation, sorrow on account of the irreparable evil which one occasions.