“Knowing when you should have your mouth shut is often more important than to open it in the right time.” – Malcolm Forbes
In short: if in doubt, shut up.
In my experience this is especially important in relationships. Easily the ego puts words in my mouth that I later regret. As the great Dale Carnegie said in “How to Win Friends and Influence People”: You can not win an argument.
However the discipline of keeping your mouth shut has another huge virtue: to allow the opening of the ears.
And, with my ears open, I usually learn something.