Has Grothendieck ― runs the obvious question ― gone mad?
Well, possibly. It all depends on what you mean by ‘mad’.
‘He lives alone and he writes on really deep ideas,’ says Schneps.
‘In the past, what about saints or prophets? Did people think they had gone mad?
He cannot bear to live in the world we’re in.... He’s certainly abnormal.
I could not possibly call him mad. People say there’s normal and there’s insane.
These are not the only two categories....’
http://www.lewrockwell.com/spectator/spec262.html