I AGREE!,,, RIGHT DOWN TO THE BLOODY GROUND!!!,,,,FRIENDSAslan said:pretty much right on the head.
Also ignore any bs about a "useful blade". Even the shortest of blades can do serious damage if used properly.
A lot of tissue is elastic, which means you can jab and slash with a very small blade and cause a lot of destruction.
Take your thumb and press into skin. Now imagine a 1/4" blade sticking out past the end of your thumb - how deep or how much tissue would you be able to cut?
Any size knife is useful - or at least can be. In fact a short knife can be an advantage if your opponent is unaware of it.
When faced with an opponent who has a knife, you will get cut. You do have some control over how badly and where.