Why do illnesses exist?

Like, did nature suddenly just go, "OH HEY, LET'S MAKE THE HUMAN'S LIVES SHIT!" And then create diseases and stuff?

Well, we don't need you nature!!!! HAHA!!!! (well we do but let's not talk about that...)

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Eat ass, smoke grass and sled fast.
SLED GANG!

(Ps. 50 chapters!!)