I've pointed out on numerous occasions that to use a handgun for defense requires putting effective rounds in the right place to stop the attacker. Put ineffective rounds into someone, and they probably won't have the desired result. Similarly, put effective rounds in the wrong place, and they won't shut him down.
This was illustrated very graphically in a recent attack by a Palestinian on a bus stop in Israel. Watch the footage below. WARNING: It's graphic! You'll see the Palestinian crash his car into the bus stop, exit the vehicle wielding a machete, and attack those sitting in the bus stop. A passerby draws his pistol and engages the man, but he keeps on renewing the attack and/or trying to get away. Some reports I've seen indicate that he was shot again on each of those occasions, incurring up to a dozen bullet wounds, but until the end he kept on fighting, struggling and moving. Clearly, the rounds did not do an adequate job, for whatever reason.
A corollary: one single head shot through the brain would have ended the problem right then, right there. I have no idea why the man with the pistol didn't do just that. He was close enough to be sure of his target. If I'd been in his shoes, that would have happened the moment the Palestinian first sat up to reach for the machete . . . and it wouldn't have happened only once.