Counsel in the heart of man is like deep water; but a man of understanding will draw it out.
The words of a man's mouth are as deep waters, and the wellspring of wisdom as a flowing brook.
They search out iniquities; they accomplish a diligent search: both the inward thought of every one of them, and the heart, is deep.
1 Corinthians 2:11
For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God.