We keep hearing this tired line from 9mm fans, who use it to champion their favorite caliber against more powerful ones, like .40, .45, and .357. Yet they don't put their money where their words are, and use mousegun calibers, because they know in their hearts that in reality shot placement isn't the only thing that matters -- penetration, stopping power, bullet design, weight, and diameter all matter too. All these factors go together, along with the qualities of the target, to determine the outcome.
Shot placement is what matters once you have a cartridge that can reach the vitals even through appendages
. I would bet my life savings that you would not be able to tell the difference between the 38caliber 9mm or the 45caliber 45acp that just entered between your nipples. Once a minimum power factor is achieved shot placement is key. A hit from the mighty 45acp to the abdomen vs. a hit from the lowly 9mm to the heart, guess what 9mm wins.
BTW I'm not a 9mm champion. I shoot both 9mm and 45acp. Carry the Glock 30 for CC.