system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If people can surgically have half their brain removed, then how come, if shot through one half of the brain, we die instantly?

So there is a surgical operation that people can have called a hemispherectomy where in people who suffer from major seizures and other such symptoms can have half of their brain, one hemisphere, removed and can still function relatively normal. However, if I took a gun, aimed correctly and shot myself (or anyone for that matter) through exactly one hemisphere of the brain, I (they) would die instantly. Any thoughts as to why?
gpt
For similar reasons why we can remove a whole's leg via surgery, but if you get it chopped off with a rusty machete, you'll bleed out in a matter of minutes. A surgical procedure is done with careful precision in order to avoid disrupting major blood vessels, which can otherwise cause massive bleeding is severed. The major trauma induced from gunshot wounds also cause major swelling along with the bleeding, which puts pressure on the brain and can disrupt normal neurological functions (ie - breathing) as well as a host of other things that can be medically described as 'very bad'.

Also, a gunshot wound through one hemisphere might not necessarily kill instantly. If it doesn't destroy the brainstem, the most inner part of the brain, you're body could still perform some basic functions that can keep you alive for a short time (until the bleeding and swelling causes your brain to shut down).