If someone says we can never stop sinning, especially from another believer, point blank, then pause and begin to explain it with scripture. Hopefully you are ready and know how to proceed. This can be a daunting task.
The video you provided explains a good plan to follow and execute that will really help in explaining why a believer cannot and will not choose to sin as a habit of the old person, or flesh. A Christian is directly influenced by his new seed and spirit.
I would make it a real project to investigate how you would explain it, with familiarity of pertinent and logically drawn scripture. This takes training and the help of God to guide you, or anyone contemplating it, with a real interest in this subject.
I've attempted to explain it to others before, and it really comes down to the knowledge base of both parties and their motivations in the Spirit to understand the subject and apply it in their lives.