Jer. 17:9 273 times in WT publications (1950 to 2011)
Pr. 3:5 581 times
Both in an article: 117 times
One thing Jesus emphasized was that the religious leaders of his time did not trust the "common" people to be able to read the Law and make application without additional interpretation, the Talmud.
(Matthew 15:1-9) . . .Then there came to Jesus from Jerusalem Pharisees and scribes, saying: 2 “Why is it your disciples overstep the tradition of the men of former times? For example, they do not wash their hands when about to eat a meal.” 3 In reply he said to them: “Why is it YOU also overstep the commandment of God because of YOUR tradition? 4 For example, God said, ‘Honor your father and your mother’; and, ‘Let him that reviles father or mother end up in death.’ 5 But YOU say, ‘Whoever says to his father or mother: “Whatever I have by which you might get benefit from me is a gift dedicated to God,” 6 he must not honor his father at all.’ And so YOU have made the word of God invalid because of YOUR tradition. 7 YOU hypocrites, Isaiah aptly prophesied about YOU, when he said, 8 ‘This people honors me with their lips, yet their heart is far removed from me. 9 It is in vain that they keep worshiping me, because they teach commands of men as doctrines.’”
*** w06 1/1 p. 23 par. 16 How Firm Is Your Trust in God? ***
Modesty: The Bible says: “Trust in Jehovah with all your heart and do not lean upon your own understanding. In all your ways take notice of him, and he himself will make your paths straight. Do not become wise in your own eyes.” (Proverbs 3:5-7) Sometimes, a certain course might seem practical from a secular point of view. (Jeremiah 17:9) Still, a sincere Christian looks to Jehovah for guidance. (Psalm 48:14) ‘In all his ways’—in congregation matters, education or secular work, relaxation, or anything else—he modestly seeks Jehovah’s counsel.—Psalm 73:24.
*** w01 8/1 pp. 9-10 par. 11 Can You “Distinguish Both Right and Wrong”? ***
The fact that God called to account those ancient Jews who became “wise in their own eyes” makes it all the more important for us to avoid relying on ourselves in determining right and wrong. Many people today subscribe to the notion of “just listen to your heart,” or “do what you feel is right.” Is such an approach sound? Not according to the Bible, which plainly says: “The heart is more treacherous than anything else and is desperate. Who can know it?” (Jeremiah 17:9) Would you rely on a treacherous and desperate person to guide you in your decision making? Hardly. If anything, you would probably do just the opposite of what such a person tells you. That is why the Bible reminds us: “He that is trusting in his own heart is stupid, but he that is walking in wisdom is the one that will escape.”—Proverbs 3:5-7; 28:26.
But should Christians be checking that which others teach them?
*** w10 9/1 p. 13 Guard Against Being Deceived ***
You have nothing to fear from examining your beliefs in this way. In fact, the Bible encourages you to “make sure of all things” before accepting them as true. (1 Thessalonians 5:21) Toward the end of the first century C.E., the apostle John urged his fellow Christians: “Beloved ones, do not believe every inspired expression, but test the inspired expressions to see whether they originate with God.” (1 John 4:1) Yes, even though a certain religious teaching seems to be “inspired”—or to come from God—it is still the course of wisdom to examine the Scriptures to make sure before accepting it as true.—John 8:31, 32.