He that trusteth in his own heart is a fool.
The heart is deceitful above all things.
So you don’t think you can do something wicked? Dream on! Don’t trust in your own heart. As Jeremiah said, it’s “deceitful above all things, and desperately wicked.” You can actually take something that is wrong and persuade yourself that it is right. Then you can do it without a bad conscience. That’s how wicked your heart is. Trust in the Lord - don’t trust in yourself.