Knives do not immediately incapacitate – often, a person who has been stabbed is able to continue fighting for long enough to successfully retaliate, even if they die soon after. This makes knives both a poor choice for self defence, and a good choice for murder. A horrific way to fight since ancient times.
An important point to learn from this video: striking is an effective response to a knife attack, assuming that you are a capable striker. Many people tend to focus on the knife and fight to control it, not realising that this is as good a time as any to punch the face.