In my online course on the Johannine Epistles, we were looking at the apparent contradiction between 1 John 1:8 and 3:6 this last week. The first texts states: 'If we say that we do not have sin, we deceive ourselves and the truth is not in us.' 1 John 3:6 says, 'Everyone who remains in him does not sin. Everyone sinning has not seen him or known him.' Ultimately the context of these two passages is important for understanding what is being said. Both are in a context that mentions the importance of living or walking as Jesus did, imitating him.
The other piece from both passages, especially 1:8, is that everyone sins. The New Testament makes clear that sin is part of the human condition (Rom 3:23). I just ran across an interesting passage from the Testament of Abraham which makes this same point. In chapter 10, Michael the archangel takes Abraham on a tour of the world. As they travel along, Abraham sees various sins taking place or about to take place--men sharpening swords, sexual immorality, and robberies. When Abraham sees the sins he calls on God to destroy the sinners, and God does so. After the third time this takes place, God says to Michael: 'O Michael, Commander-in-Chief, command the chariot to stop and turn Abraham away, lest he should see the entire inhabited world. For if he were to see all those who pass their lives in sin, he would destroy everything that exists' (10:12-13). This raises a number of other questions, but the point of this statement is clear: everybody sins or has sin. The Second Temple Jewish text of the Testament of Abraham has a similar view of humanity as does the New Testament.
Citation from E.P. Sanders, 'Testament of Abraham', Old Testament Pseudepigrapha vol. 1.