In defending, the attacker never sees the knife of the defender. It is shielded by the body of the defender until it is used to defend.
Let's be realistic here. Thats taking a
gigantic leap in faith that you see the attack coming.
You are far more likely to get bashed over the head from behind than having a knife covertly at the ready awaiting imminent danger.
Even if attacked openly, the chances of the aggressor being poised to do you harm is FAR higher than your ability to deploy any knife to save yourself from an attack.
How would you justify your actions in court? "Well officer, I knew I was going to be attacked, so instead of taking the time to flee, I took out my knife, and hid it behind me until they made a move, then I "defended myself"
They call that Man 2.
Now, can I deploy a knife and make multiple cuts on a target in a flash? You bet I can.
Would I do it if I was in a deadly struggle with someone? You bet I would.
Do I ever foresee getting into a situation where I would need to be an expert at doing so? I sure dont.
Phil, you mentioned statistics. How many people defend themselves successfully against an attack with a knife? I don't know the answer, but I would say its probably 50 times less likely than self-defense using a firearm, and hundreds of times less likely than leaving yourself in a vulnerable position, or being able to escape without the confrontation escalating.
I can think of one single case that I have read about in the last 15 years of studying self-defense literature. Ayoob wrote of a case involving a man attending Harvard who was beaten by two unarmed men and killed one of his attacker while defending himself with a Spyderco Military. He was charged with Manslaughter.
I have nothing against training in martial blade craft. But to think that it will save you in a typical physical confrontation is poor judgment. An unarmed opponent who is better trained in UNARMED combat will likely disable the average "self-defense knife user" and use his weapon against him.
Don't rely on anything that you are not well trained in, and don't train on that which is unlikely to save you.