When somebody goes outside the cultural norms, the culture has to protect itself.

If you stare at a wall from four in the morning till nine at night and you do that for a week, you are getting pretty close to nothingness.

Even in the presence of others he was completely alone.

That's the classical mind at work, runs fine inside but looks dingy on the surface.

A culture-bearing book, like a mule, bears the culture on its back. No one should sit down to write one deliberately. Culture-bearing books appear almost accidentally, like a sudden surge in the stock market. There are books of high quality that are a part of the culture, but that is not the same. They are a part of it. They aren't carrying it anywhere. They may talk about insanity sympathetically, for example, because that's the standard cultural attitude. But they don't carry any suggestion that insanity might be something other than sickness or degeneracy.

If there were only one person in the world, is there any way he could be insane?

What is essential to understand at this point is that until now there was no such thing as mind and matter, subject and object, form and substance. Those divisions are just dialectical inventions that came later...They are just ghosts, immortal gods of the modern mythos which appear to us to be real because we are within that mythos. But in reality they are just as much an artistic creation as the anthropomorphic gods they replaced.