Paul talks about his conscience. It is my belief because of what I experienced when I received the Holy Spirit, and confirmed in scripture, thirty years after being a so-called Christian, that my conscience became super-sensitized. And I could feel His presence guiding me, but also empowering me. It is a matter of walking in truth. I believe that both Jesus when He said "Be perfect," and the apostles, when they said, "My children I say this so you will not sin," and also in the same epistle, "we cannot sin because of the seed of the Father in us," that it IS possible.
There is life and death in the power of our words. So, I also think we should be saying IF we sin, and not WE WILL sin. There is a huge difference in polarity of positivity and victory vs. negativity and defeatism. If you are doing well, but someone keeps telling you, you are a failure, and if you believe their negativity about you, you will act it out. Paul not only taught that we are dead to sin, he also taught us to get that truth into our mind and RECKON ourselves dead to sin.
When we have been cleansed of all sin when we are born again, and given the power of the Holy Spirit, we go from death to life - from sinner to son. John 8:34-36. Some believe what false teachers promote that we will always be sinners, even after being cleansed, and empowered, and teach it is humility to consider yourself a sinner saved by unmerited favor, but that is false humility, and a slap in the face to the power of the blood of Jesus to take away our sin, not just cover it up but it is still there. The true meaning of grace according to the Semitic writing style of Jewish writers is grace is the power of God given to you to make you free from sin, not free in spite of continuing sin. That is what Jude 1:4 is about - turning the grace of God into lasciviousness.
So when I see someone saying negative beliefs, as if 1 John 1:8 is about a Christian, and not a non-Christian in self righteousness before Christ and before 1 John 1:9 (read together) and being cleansed of all sin, I cringe, and wonder where that doctrine started.