It is not good to lean unto one's own understanding (or self). We must learn to trust God. We are to be like children in our trust in God but we are not to be like children in knowledge. Many professing christians are refusing to believe that God through the Holy Spirit in the Word really can give accurate understanding of crucial matters. This is the knowledge that God gives in regeneration. It is divine in origin, it does not originate from human intellect. This knowledge affects the whole being of the blessed man who receives it. And this whole man (head, hand, feet etc) are to use this gift to SERVE GOD AND NEIGHBOR.
But there are some that despises this knowledge and unwisely chop up the term knowledge into a heart and head section. Instead they look to some "mystical", murky place, either in themselves or up in the blue, that they call "heart" which they set their hope to. Wrongly thinking in vain that there's a huge gulf between "heart" and "head". This is nothing but unbiblical human sophistry and pietist nonsense which crept in relatively late. Much of it stems from romanticism, a philosophy that became popular in the 1800s.
The Bible says that man thinks with his heart and that which his mouth speaks (and how he acts) shows his heart. From that we can also judge/discern (up to a point, I must add) what is in a man's heart. If someone for example is teaching heresies or speaking lies in hypocrisy or continually are making unrighteous judgments - then his heart is not "right". Examples of this is found in scriptures like Prov.23:7, Ezk.38:10, Luke 9:47, 2Tim.3:8 and Tit.1:15 etc.
The Bible does not make any dichotomy between heart and head, they are to understood as being one. Scriptural examples of this would include Gen.6:5,24:45,27:41, Exo.8:15,35:35,36:2, Deut.2:30,11:18,15:9, 1Kings 3:9, Ps.14:1,15:2,49:3, Prov.2:10,14:10, Eccl.7:22, Isa.33:18, Dan.5:20, Matt. 13:15, Luke 1:46-47,2:19, Acts 8:22, Rom.1:28,10:9-10 Phil.1:27 and Heb.4:12 etc.
Insisting that there is a gulf between heart and head leads to a foolish rejection of knowledge and instead comes a dependence upon feelings and "experiences", and thus a false standard. Now, if you lack knowledge in a field what do you have in its stead? Ignorance! Do a search in the Bible and look up what it says about knowledge vs ignorance. It doesn't take a scholar to spot that it says much about knowledge in the positive and much about ignorance in the negative. An undisputable fact is that these two words are actually often marked as indicators of being saved vs being lost. We're talking about very serious stuff here! However, there is a saying of Paul, in the context of not eating meats offered to idols, that knowledge puffs up while charity edifies. Needless to say, unless knowledge is acted upon in love it bears not the fruit intended. There is no difference there from faith.
Sometimes you will hear notions that the Pharisees were "religious experts" of their day and supposedly had a lot of "knowledge". Views like these are not uncommon but have no ground in facts. Although they were very zealous about their worship, they actually lacked knowledge. In reality they had gone astray from the path of the Saints of old and Jesus rebuked them for NOT having applicable knowledge (Luke 11:52). Paul likewise said that the unbelieving pharisees were indeed zealous for God, but not according to knowledge and that they were ignorant of God's righteousness (Rom.10:2-3). They were certainly sincere and commited in their zeal - but they were ignorant about that which was crucial and therefore - lost. This same thing is a reality today in christianity.
