Everything, Literally everything is controlled by your brain, like your hand movement, you speaking, all of them. it’s impossible what you’re saying “My brain is working full time, but my mouth never works” since your brain controls your mouth and tells you when to speak. It’s just that doubt/anticipation that makes us stutter more. And don’t worry there are plenty of jobs available more. Once you master the NOT GIVE A FUCK mentality you become unstoppable. Heads up bro. Don’t forget,You’re Batman.