Self Deceit is probably the worst kind of deception because it is self-inflicted.

Though we are all susceptible to being burned by trusting others we aught to be able to trust ourselves, shouldn't we?

I guess not.

Actually, Jeremiah was talking about the Heart that has not been Transformed through the renewing of the Mind (Rom 12:2.) He was talking about the SinNature.

When you have been purged of an EvilHeart and have come into awareness of the PerfectLawOfLiberty you have Power to overcome self Deception.

Self Deception works through Idolatry - thinking more of yourself than you do of God - considering your will above His Will.

So, to the extent you have submitted your Heart to what you Know in your Mind you avoid self Deception.

This is where Meditation comes in. What you Know in your Mind (assuming it is from Hearing the Word) should be meditated on, digested, so that that it purifies your Heart.

As your Heart (the joining of Spirit and Soul) is purified you begin to live in the PerfectLawOfLiberty and operate in the Power of the HolySpirit.

Stop believing in your Mind what you are unwilling to believe in your Heart. This state is DeceivingYourOwnSelves.

If your Mind tells you it is Truth (Joh 17:17) then Believe it in your Heart.

The proof that you Believe in your Heart is that it changes how you act. This is James' point in Jam 1:22 .

Jesus said this: of the Abundance of the Heart his Mouth speaks. - Luk 6:45. So what we speak is evidence of what is in our Heart.