1John 1:5-7) What is the result when a Christian walks in darkness, that is, continues willfully to do what he or she knows to be wrong? How does this involve self-deception? What is the result, according to verse 7, when we walk in the light? How do we get back into the light if we sin?
When we accept Christ into our heart and become a Christian, we start to learn how we should live our lives as one by knowing (by listening to preaching) and studying The Word. The Holy Spirit (through our conscience) will quicken our spirit if we do anything wrong. However, having say that, we often do see and/or hear of christians who are very well versed in God's Word and still walk in darkness and try to justify their ways and wrongs. They are in denial. They try to make their own Will into God's Will. This is self-deception.
On a personal level, we can only get back into light if we sin by confessing our sin(s) to God and ask and pray for forgiveness and show true repentence. If possible, it is good to have a mentor to walk and guide us to walk more and more back into God's way and light.