Autoimmune diseases are proof that your body is a fucking idiot.
The best thing I can compare it to is a dog catching a glimpse of itself in the mirror and barking insanely at the intruder while trying to kill it. Your body basically does the same thing.
Or like an episode of Criminal Minds I saw recently where a man was suddenly stricken with paranoid delusions, didn’t recognize his own parents, rather suspecting them to be imposters, and then went on a killing spree – starting with the parents.
Body: “Hey! HEY! JOINTS! FUCK YOU!” *attacks with a claw hammer*
Your nerve endings: “No…NO NO NO, THAT’S PART OF YOU. YOU IDIOT, LEAVE IT ALONE!”
Body: “NO, I AM GOING TO END YOU, MOTHERFUCKER! YOU ARE DEAD, YOU HEAR ME? DEAD!”
Joints: “Wait…what? What the hell did I do!?”
Body: “Waaaait a minute….HEY, WHAT THE FUCK IS THAT?”
Nerve endings: “What? That’s myelin – it’s what protects me! Don’t even start on that, you moron, I NEED that to function properly! It’s like armor. I’m totally fucked without it.”
Body: “BULLSHIT! I’M SETTING IT ON FIRE!!!”
Nerve endings: “You realize that you did this last week and that’s why you keep dropping wine bottles in the grocery store parking lot, right? You keep it up, and you’re going to end up pissing yourself and wondering why. People already think you’re drunk half the time.”
…it’s all sorta like that.