Yup, it’s pretty bleak and he is honest about that.
When someone is coming at you and he is right up in your face going “stabstabstabstanstabstab” there are things that MIGHT work, but nothing can be relied upon to work with consistency, and then you are dead.
That does not mean you shouldn’t try to train them. But be honest with yourself. It is bleak.
I would never tell anyone that knife defense is 100% effective. It depends on too many factors. One of the most important is training of course, and along with that getting a person used to the fact that being attacked with a knife is scary, and they need to overcome that. That may lessen the chance an attacker has to get into his comfort zone of controlling you, like grabbing you or placing his other hand disadvantageously to you.
@Buka have you trained any specific art's defenses? I have seen many techniques that seem effective, but usually depend on both speed and agility.