God knows us better than we know ourselves. He's aware of our weaknesses, the memories of sins that seem to predispose us to fail again and again. He knows our heredity and upbringing, the past and present influences that push us in the wrong direction. J. I. Packer calls these the "latent forces" of our existence as well as the "patent facts."
At my stage of Christian growth, I struggle with attitudes and actions over which I seem to have little control. I identify with Dostoevsky, who said, "It is nature asserting its rights." Paul called it "sin that dwells in me" (Romans 7:17). It has made me guilty of much, and capable of much more. That's why my heart sometimes condemns me, even though I'm a believer.