Proverbs 20:5

Counsel in the heart of man [is like] deep water
Pure and undisturbed, but secret, hidden, and hard to be come at: such are the things of the spirit of a man, the thoughts of his mind, the devices of his heart; which, though easily known by the searcher of hearts, are not easily penetrated into by men; or it is not easily got out of them what is in them, especially in some men, who are very close and reserved. This is true of wicked men, who seek sleep to hide their counsel; and of good men, especially studious men, who have got a great deal of wisdom and knowledge in them, but not very communicative, being slow of speech, and silent in conversation; but a man of understanding will draw it out;
he will find ways and means to discover the secret designs of wicked men, whether against church or state; and, by asking proper questions, an understanding man will get out useful things from men of knowledge, the most reserved: some men must be pumped, and a good deal of pains must be taken with them, to get out anything of them, as in getting water out of a deep well, and which when got is very good; and so is that wisdom and knowledge which is gotten by an inquisitive man from another of superior knowledge, but not very diffusive of it.