John Gill Commentary Proverbs 17:28

"Even a fool, when he holdeth his peace, is counted wise; When he shutteth his lips, he is [esteemed as] prudent." — Proverbs 17:28 (ASV)

Even a fool, when he holds his peace, is counted wise Not only one that is sparing of his words, and is really a man of knowledge and understanding; but even a fool, if he is but silent, and does not betray his folly by his words, will be reckoned a wise man by those that do not know him; and, whatever fool he may be in other respects, yet in this he acts the wise part, that he holds his peace and says nothing.

[and] he that shuts his lips [is esteemed] a man of understanding and keeps them shut, lest he should say anything rashly and hastily; a man that has so much command of himself as not to speak unadvisedly, through the heat of his own passions, and through the provocations of others, will pass for a man that understands himself, and knows how to behave well before others.