John Piper, Taste and See: 140 Meditations (Sisters, OR: Multnomah, 2005), 28:
One profound biblical insight we need to know is that our heart exploits our mind to justify what the heart wants. That is, our deepest desires precede the rational functioning of our minds and incline the mind to perceive and think in a way that will make the desires look right. It is an illusion to think that our hearts are neutral and incline in accordance with cool rational observation of truth. On the contrary, we feel powerful desires or fears in our heart, and then our mind bends reality to justify the desires and fears.