The purpose in a man's heart is like deep water,
but a man of understanding will draw it out.
Every counselor should know this verse by heart. But the skill is not reserved for professional counselors. It is for anyone with understanding - understanding of what? The biblical teaching about the human heart. That it is sinful and deceptive even to the owner of the heart. That even the redeemed heart will have vestiges of sin which will inflict the owner until he is received into glory. That, nevertheless, all individuals are created in the image of God and receive a measure of God's common grace, so that as wicked as they may be, they also possess great potential for creative, intelligent, even kind acts.
Understanding biblical teaching about the struggle against the flesh, the world, and the devil – all three are at play tugging at an individual's heart. Every decision he makes is either a giving in or a standing against one or all of these three.
Understanding the ways individuals have developed to protect their hearts from being examined by others and even themselves - the defenses they put up, the masks they wear, the rationalizing they do, and so on. It is understanding their fears, what motivates them, what arouses them and discourages them.
It is understanding one's own heart and what one needs to do to patiently listen, to love the other person, to let down one's own defenses and be attentive.
A man of understanding is like a good fisherman fishing in deep water. He quietly, patiently, and knowledgeably casts his line and waits.