It is God's mercy to us that our conscience has the added power to condemn us if we go past that warning. That guilt is meant to soften the heart we had to harden in order to do what we knew was wrong. The conscience is God's plumbline in the heart of man. Knowing the Right Thing to Do Sin is not just the wrong things you do. It is knowing the right thing to do, but not doing it.
Sin is self-centeredness.
Every evil thing stems from this root.