A story prompt if you like.
Moriarty. What made him go mad?
Because he is mad, and, God help us, not in a good way.
FYI: I'm bipolar myself, so yes, I do know people can be mentally ill. But I also believe people can go insane.
There's a lovely series by Barbara Hambly... in it, one madman explains what happened to him.
He is wicked, evil, cruel, and in no way a nice person. But you feel for him then. You grieve for what happened to him. It makes me wonder, could something have happened to JM? What would it have been??
Insanity is when 2 + 2 does not equal 4, but instead equals 5.
In other words, when reality cannot be explained as it normally is, or by the usual rules. When your reality doesn't match what everyone else perceives.
So if anyone writes something about this, I'd be fascinated. Possibly horrified too, but that won't stop me from reading.
SPOILER WARNING: I love the Antryg Windrose Chronicles. Particularly Antryg himself. Don't read anything about them beforehand if you don't want to be spoiled! And yes, people do talk about things while reviewing Book 2 which WILL spoil Book 1.
If you have read the series, someone wrote up a diagnosis of Antryg. There is fanfic about him and his world, which I did not know.