1) You pull the gun and pull the trigger, and nothing happens. Dead battery. Your attacker kills you.
2) You get wounded. Your own blood runs onto the sensor. It stops working. So does the gun. Your attacker kills you.
3) You have gloves on. The gun can't see your fingerprint. Your attacker kills you.
4) You take the gloves off, and its so cold you get frostbite and can't pull the trigger. Your attacker kills you.
5) A strong radio field interferes with the electronics in the gun. It won't fire. Your attacker kills you.
6) The gun gets wet, the waterproofing fails on your now 80 year old gun, it doesn't fire. Your attacker kills you.
7) You leave your gun in the car, its temperature reaches 190 degrees. The electronics won't work at 190 degrees. Your attacker kills you.
8) The electronics simply fails for any number of reasons. Your attacker kills you.
9) You're wounded. You throw the gun to your wife / friend / lover to continue the defense. It doesn't recognize their fingerprints. Your attacker kills you, rapes her.
10) The electronics fails. You get it repaired. Now it works sometimes, doesn't sometimes. The tech can't find the problem. Your attacker kills you.