1 John 1:8-10 (ESV)
If we say we have no sin, we deceive ourselves, and the truth is not in us.  If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.  If we say we have not sinned, we make him a liar, and his word is not in us.
What commentary is needed here? Saying we have no sin, we deceive no one but ourselves. But this is what we would do. Deceives ourselves, and deceiving ourselves deprive ourselves of forgiveness. This is what man does, we think we can hide our sin with a fig leaf, and we hide it from no one but ourselves. The first lesson a Christian learns is to see his sin for what it is. We don’t ever mine the depths of our sin, we can’t even get to the point where we can see them all, at some point you just see that you are a sinner through and through. Not just in the big things, but such tiny things become such great sins when you examine them. Our attitudes, our selfishness the way we carry ourselves is so often such greater sin than even the sin we are trying to hide with our façade.
Yet if we just confess our sins, see them for what they are, then Christ forgives them, and forgiving them we takes them from us in such a way that we no longer have to carry them under the fig leaf of self-righteousness.