Hey, 'not sure' is supposed to my guiding star! I may have lapsed here, and absolutely agree that we should not define activities that deviate from normal human behavior as mental illness. On the other hand one should not romanticize and define as normal or unproblematic that which is a mental illness either.

Granted I could have dug further. To my defense I just echoed a quote in the article, which states he held a resentment that "eventually metamorphosed into a paranoia which is evident in the pages of Récoltes et Semailles. - Excerpt, "The IHÉS at Forty" by Allyn Jackson (1999)".

I did however do some digging in order to produce this response to your comment, and I found an interesting article about Grothendieck on Psychology Today [0]. It also mentions an apparent trend among some mathematical geniuses to develop mental illness, and it expresses hope that a connection may be found thanks to "advances in the nascent field of creativity-psychopathology neuroscience", of which I know nothing. But I stick to my original speculation: that overworking might be part of it (until I'm convinced otherwise).

As for Grothendieck the author has this to say about the later stages of his life: "He believed himself to be in communication with Plato and Descartes, and even with God himself. The belief in signal transmission is a signature psychotic delusion".

[0] https://www.psychologytoday.com/us/articles/201707/the-mad-g...