We are told to not lean on our own understanding! It's not that we don't have an understanding, nor that we don't need understanding, but it is not our understanding we are looking for. We are looking for God's understanding, which is certainly helped by reading the Scriptures, but it is also explained in the Scriptures that it is not us the Spirit of God that has the correct understanding.
Luke 12:31, 32 But seek for His kingdom, and these things shall be added to you. Do not be afraid, little flock, for your Father has chosen gladly you give you the kingdom.
So the kingdom is something you seek for. As previous pointed out, Jesus explained to Pilot that His kingdom is not of this world, and if it was there would be those that would be fighting for Him at that time. We read in many places about His angels and that they are ministering spirits, (Heb 1:14) And we also know this kingdom is in our midst. So we should realize we have a King (Jesus Christ) and He has a kingdom that if sought can be found. So we can find it and if we have indeed found the King and His kingdom we certainly should have an awareness of all this. And if found and are now under the King, getting instructions and understanding from Him and His ministering angels, then are we not now a part of it. And if we can talk to the King are we not now interceding as a nation of priests and part of that Kingdom. But if unaware of that Kingdom, how does anyone say they are a part of it. Perhaps they could say "As I understand" meaning they have read the Bible and have an understanding of it, and perhaps they have also been reading the teachings of other men who have done the same as them. But that is all leaning on our own understanding.
Prov 7:4 Say to Wisdom, "You are my sister", and call understanding your intimate friend
We know that the Spirit has wisdom, but do we listen. And we sing a song that goes, "What a friend we have in Jesus", but do we really know Him and listen to what our King says?
He once told me, "Karl, they call me 'Wonderful Counselor', but I am not a wonderful counselor to those that don't listen to Me."
Now as I understanding it, from conversations I have heard with my spiritual ears, there is this wonderful King in the heaven who has a heavenly kingdom of which I seek, find, and have become a part of as a result. And they (the King and His kingdom) are wiser than men.