The meaning is that if you are not sure of the accuracy of what you are about to say, then it is better to remain silent, because giving an answer that is inaccurate will prove you wrong, while remaining silent will leave the accuracy of your non-answer in doubt.
The meaning of this saying is fairly clear – many of us have not raised our hands in class to give an answer, or have said nothing while in a meeting or brainstorming session, because we didn’t want to look like an idiot. No one wants anyone else to think that they are stupid; in general, we want others to think the best of us, and looking stupid in front of others doesn’t further that end.
On the other hand, if you speak, then you give them information to judge your thinking on the matter. And if they find your words foolish, then they know you are a fool.
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