A ball point pen, properly aimed into the eye, will reach the brain if driven home with sufficient force to hurt your hand. The key is aim and don’t hold back ... put that pen where the brain can get the message. A book slammed edgewise into the front of the throat will stop the wind of all but the largest vermin. A set of keys ... well, you get the picture. Do something, don’t play the part the attacker has planned for you. If you allow the attacker to control you, you are dead anyway.
A lot of people will hold back.
When I tried to teach my wife how to throw a punch, she kept repeatedly throwing the worst possible punch even when I’ve seen her use strength and hit hard when scared. Getting her to let loose at will was just about impossible.
Some folks just have too much conditioning to hold back and it’s hard to break through.