In comparing translations I find that the KJV comes close but the English Standard Version gets this one best,
(Proverbs 29:11 ESV) A fool gives full vent to his spirit, but a wise man quietly holds it back.If we were looking at schools of philosophy we might find this idea in the Stoics. It should be a common understanding among Christians but because we listen to pagan psychologists we tend to call this kind of person repressed.
It is not Christian to “let it all out”. It is not Biblical to “speak your mind”. It is foolish. Now I admit that many who call themselves Christians are foolish, but that is not the standard that God has set for us.
So? Don’t say what you think. At least wait until the Holy Spirit has a chance to refine your words to express truth through love. The object is not to defend yourself but to glorify God.