Lynn Young Sensei had a question; Here is the first part of my answer. Depending upon the response we get I may have more to say.

Regarding a knife attack reality video, Lynn Young Sensei asks:

"Everyone shares these clips saying this is what it looks like are you ready? How are you training?.

On one side the attacker really does a good job and selling what would happen. Now here is the problem I see with training this way.
What is the defender supposed to do? If you really want to stop this attack you have to stop the guy. Meaning knock his block off or stun him. How do we do this in training?

Take the knife out of the equation. Lets say this same guy attacks the same way but pounding the mess out of you. It's really no different. He would beat you to death. I just feel like clips like this are really one sided. I hope I am making sense."

Thanks for always asking the easy question, Lynn.

I could pop off with the stock answer "you fight the way you train, so train the way you fight". The problem with this approach is as you said, someone is getting hurt. The real answer has to be much more complex.

Traditional martial arts training has been developed over many centuries to answer just exactly the question you ask, and the answer lies in the hierarchical nature of traditional martial arts.

One uses kata (poomse, patterns, call it as you will) and/or ippon/sanbon/gohan/jiyu-ippon/kaishi-ippon kumite/kumitachi to train the body with muscle memory and conditioned responses. One uses jiyu kumite/kumitachi to develop speed, accuracy and timing. In all of these one must perform their own training against someone at least three ranks higher than themselves or there will be no progression.

Hirakawa Sensei was 86 years old when I began training with him and I could not so much as lay a finger on him unless he stood still and let me, which typically resulted in me falling upon my little head again. When I received my certificate of competency I was managing a whopping 20% (give or take) success rate and two months before he passed away at 94 I had made it up to a rocking 40% success rate (more or less). I improved because my opponent (Sensei) was that much more skilled than I was, and would press me just as hard as he possibly could without permanent injury. I had to get faster, I had to get stronger, I had to hesitate less as time went by (because I really do not like being smacked upside the head with a bokken).

Another rambling reminiscence from an old man: Not too long ago I decided to practice gohan kumite with a 5th kyu student. All I did was stand there and block the attacks while encouraging the student to go faster and strike harder. By the time we were done the student was going just as fast and as hard as they possibly could and I was blocking at the last possible instant without getting hit (I do not like being hit any more than you do). I also watched the expressions and body language go from fear, to excitement, to enjoyment, to understanding of the techniques we were practicing. I sincerely doubt this would ever occur had they been practicing against someone of their own skill level; only by forcing them to work as hard as possible while allowing them to work without concern for my safety did we achieve this highly desirable result.

Think about it: White belt kata are not taught by other white belts and white belts should not practice kumite/kumitachi against other white belts. It serves no purpose.

If you wish to learn then find someone higher ranked to train against. Remember that helpless, frustrated feeling from the first time you had to spar someone much better than you? Remember that desperate desire to land "just one hit"? Find someone that makes you feel that way again and train against that person. If you progress past that feeling then move along and find someone else who brings it back again.

By the same logic, one should strive not to refuse training against lower ranked students. It is your job as their senior to correct their technique, press them as far as they can go and help them progress. However, do not allow this to harm your own development. Unless you have been specifically directed to train a lower rank it is always permissible to say "not now, I must see to my own training".