In high stress situations people frequently don't even realize they got shot until after the adrenaline wears off. In my EMR course they trained us that we need to physically check for bullet wounds ourselves if a shooting was suspected because you can't rely on the victim knowing that they've been shot.

That's why mag dumping is more or less standard practice in survival situations. Sure, 1 bullet may kill the person, but it probably won't do so for several minutes and until then you've only pissed them off. So you shoot and keep shooting until they actually drop. Which, when you're talking about a particularly wimpy round like the one above, can take far more bullets that most people expect.