1 Kings 3:9-14 So give Your servant an understanding heart to judge Your people to discern between good and evil. For who is able to judge this great people of Yours?”10 It was pleasing in the sight of the Lord that Solomon had asked this thing. 11 God said to him, “Because you have asked this thing and have not asked for yourself long life, nor have asked riches for yourself, nor have you asked for the life of your enemies, but have asked for yourself discernment to understand justice, 12 behold, I have done according to your words. Behold, I have given you a wise and discerning heart, so that there has been no one like you before you, nor shall one like you arise after you. 13 I have also given you what you have not asked, both riches and honor, so that there will not be any among the kings like you all your days. 14 If you walk in My ways, keeping My statutes and commandments, as your father David walked, then I will prolong your days.”
Or take another more concrete example - one's relationship with their spouse. I know my wife. I know her likes, dislikes. I know from the tone n her voice or the gait of her walk what she is thinking. Yet, there is a mystery side to her which alludes full comprehension. I know her enough to want to draw closer and yet she has enough mystery as a woman to make me want to know more about her.