From some things you can not defend unless you be always on constant alert. When SHTF it is another reason why it is not like some people imagine it, you simply do not know who is potential enemy.
Even today there is need for constant scanning your surroundings for possible threats, here it is usually street robberies with knife.
If someone wants to approach to me in my “personal circle” in some situations (night time, suspicious circumstances etc.) I would definitely try to stand different than usual, knife or no knife in his hands.
I have used knife in fight, in real conditions, and my moves were dictated by rage, panic, and adrenaline, without clear intention or meaning, I still was successful simply because speed (which again was dictated with adrenaline in that time ).
I prefer firearms.