I have noticed a lot of people using the term "center mass" as a desirable aim point in self-defense situations. Heck, I'm guilty of it myself, and nothing could be more wrong. You do not want to aim center mass if you want the fight to end any time soon. You want to aim center chest. Everybody stand up. Starting at your ribcage on either side of your body run you fingers along your ribs toward the middle of your chest. When you get to the middle do you feel that point at the end of your sternum AKA breastbone? If you took CPR back before it was dumbed down you probably know it as the xyphoid tip or xyphoid process. That is the lowest point you should be aiming if you want to be fairly sure the fight will end within the next hour or two. The neck is the other end of the chest. Somewhere in between is best. There are no major organs below the xyphoid tip that will end the fight right now. None. Yes, there are some major vessels down there that can end things in something resembling a hurry, but they are not usually instantly disabling. Considering the scarcity of sensory nerves in the intestinal cavity you can't even be sure pain will take your assailant out. Now go stand in front of the mirror. Where is center mass? Center mass is a lot lower than center chest. Center mass may get the liver, stomach, pancreas, or gall bladder. It will probably also get some intestines. Personally, I would rather not wait for peritonitis to set in to call the fight over.