For me this verse from the Kena Upanishad about knowing and not knowing says it succinctly and beautifully. There are a couple of paragraphs of commentary following the verse that expound on what is meant by knowing and not knowing.

https://www.hinduwebsite.com/sacreds...arama/kena.asp

II. The disciple said: I do not think I know It well, nor do I think that I do not know It. He among us who knows It truly, knows (what is meant by) "I know" and also what is meant by "I know It not."