They say that when your view of sin is slanted, your view of God's justification will be slanted too.
I remember when I first lied to my mother, there was an insistent desire to avoid pain and yet immediate guilt soon followed - I lied. I did not know the 10 Commandments yet, something told me I should have not lied and that it would have been more noble to have been honest.
Sin according to the Bible is missing the mark. When God commands, he expects us to do them perfectly. We can't unless we confine sin to actuals only, that is to external behavior. If you confine sin to the actuals then you can tap yourself in the back and praise yourself. In fact, you can even delude yourself that you are sinless for a day! Some evangelicals/pentecostals think so! If that is the case then there is a day you can make it on your own without the cross of Jesus. If you can go for one day without sinning, why can you not say that you can go for another and another without sinning.
When you consider what Jesus says - sin is not just outside behavior, it is in us. It is a condition. He says that if we thought about anger, lust we have sinned already in our heart. So sin is not just behavioral it is internal. It is not what we do/say/think that is wrong but also what we did not do/say/think that is right.
We do not sin then become sinners, we are sinners, that is why we sin. Sin is original as found in Romans 5. It is not washed or done away after baptism nor after faith in Christ (Romans 7 and 1 John 2:1-2). We continue to struggle with it and it needs to be forgiven, this God provided at the Cross of Christ, God nailed your sins and mine in his body. So we groan and are not happy and we hope one day we will no longer be in the presence of sin.