Chris replied on the post I did about this practitioner’s chi protecting him against a blade. I’ll assume you read both posts so here’s my take on things:
First off, I understand where Chris is coming from but don’t really agree with his reasoning. I’ll cover things point by point and try to make as much sense as possible (not always easy for me, please be understanding.)

Chris said:
This is the consensus view among self-defense instructors: if you are attacked with a knife, you will get cut. You should expect to get cut. Your goal is not so much to avoid getting cut, but to avoid getting killed. So next time you meet a self-defense expert, look at their arms. Do you see any knife scars? Have they even once tested their theories against a real, razor-sharp blade?
The problem with the “expect to get cut” cliché is that it leaves no room for debate. It flat out presents your blood flowing as a fact where in reality, that is certainly not always the case. I can cite a large number of friends and fellow instructors, along with a bunch of authors I know, who faced knives repeatedly and didn’t get cut. Following this logic, they don’t know what the hell they’re talking about. That just doesn’t track with me.
I also know an interesting Asian gentleman who’s nearing 60 now and started training at around five years old. He practices his knife techniques with a live blade and has in the mean time had plenty of opportunity to test the theories of his art (I’m understating big time). Last time I saw him, his forearms were not riddled with scars. So he should be clueless too if we follow that line of thinking. Again, I don’t agree.
Having scars from a knife attack means you got cut. It doesn’t mean you did a great job using the techniques you learned. It only means you got cut. Not having scars on your arms doesn’t by default make you clueless about knife defense. There just isn’t a causal link there.