The silent fool

Proverbs 17:28 - Even a fool is thought wise if he keeps silent,
and discerning if he holds his tongue.

There isn't much I wonder about in the Psalms or Proverbs, but here is one small item. I wonder how many silent fools the writer (Solomon) had met before he created this proverb. I suppose he determined that the quiet person was still a fool by his actions.