For an unbeliever, an athiest, they can be the most rational person in the world, balanced, careful, yet have a blind spot that causes partial insanity.
Here is a complete Definition of Insanity from Merriam-Webster
1With the mind of Christ of you will be less like the definition and more like Jesus... who was the only sane person who ever walked the earth. Yes that's right.... if you are a Christian, sinning is temporary insanity.
: a deranged state of the mind usually occurring as a specific disorder (as schizophrenia)2: such unsoundness of mind or lack of understanding as prevents one from having the mental capacity required to enter into a particular relationship, status, or transaction or as removes one from criminal or civil responsibility3a : extreme folly or unreasonablenessb : something utterly foolish or unreasonable
Here is what the word of God says about the mind of Christ... and how important it is to be in our right mind. The mind of Christ:
1 Corinthians 2:16 - For who hath known the mind of the Lord, that he may instruct him? But we have the mind of Christ.
We have no way to offer any direction to others unless we have the mind of Christ.
Romans 12:2 - And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what [is] that good, and acceptable, and perfect, will of God.
Conforming to the world is insanity. Finding the mind of Christ will transform you.
1 Corinthians 2:14-16 - But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know [them], because they are spiritually discerned
The natural man suffers from insanity.... he can't receive what would be sound direction, even from the Spirit of God. He has a blank spot in his spirit.
Philippians 2:5 - Let this mind be in you, which was also in Christ Jesus:
Paul is instructing the Philippians to find and culture the mind of Christ.
Paul give evidences of what is a demonstration of the insanity of not being in possession of the mind of Christ...
Galatians 5:18 But if you are led by the Spirit, you are not under the Law. 19Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality, 20idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, envy, drunkenness, wild parties, and other sins like these. Let me tell you again, as I have before, that anyone living that sort of life will not inherit the Kingdom of God.
When a person is like this, it is temporary insanity. IF they live like this they are truly insane compared to the wholeness of the Mind of Christ.
When a person is in full possession of all his or her faculties as the mind of Christ it will look like this:
Galatians 5:24 The Holy Spirit produces this kind of fruit in our lives: love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness, and self-control.
We are the ones who are instructed to do this.
1 Peter 1:13 - Wherefore gird up the loins of your mind, be sober, and hope to the end for the grace that is to be brought unto you at the revelation of Jesus Christ;
It's time to sober up... and get out of the asylum.