The tongue of the wise makes knowledge acceptable, but the mouth of fools spouts folly. - Proverbs 15:2
A soothing tongue is a tree of life, but perversion in it crushes the spirit. - Proverbs 15:4
He who guards his mouth and his tongue, guards his soul from troubles. - Proverbs 21:23
Look at the ships also, though they are so great and are driven by strong winds, are still directed by a very small rudder wherever the inclination of the pilot desires. So also the tongue is a small part of the body, and yet it boasts of great things. See how great a forest is set aflame by such a small fire! And the tongue is a fire, the very world of iniquity, the tongue is set among our members as that which defiles the whole body, and sets on fire the course of our life, and is set on fire by hell. - James 3:4-6
I've learnt that sometimes it's better to keep silence than to defend oneself.