From the section "The Creative Act: Symptom Or Side Effect"

"Does one have to be crazy to be creative?" "Nope, but it helps!" This is meant, of course, facetiously, as in: "Does one have to be crazy to have children?"

Putting aside the complex ethical and philosophical issues and all the psychological theories about mental illness, here are the commonsensical conclusions. Creativity is associated with, and enhanced by, certain personal characteristics and intense and varied experiences. There is reasonable consensus as to what these characteristics and experiences are. The characteristics are: high levels of motivation and energy and conscientiousness; substantial intelligence and an ability to find or invent connections between disparate elements; and independence of thought. The requisite experiences vary in type: they can be emotional or intellectual or actual. Regarding both characteristics and experiences, some are the result of nature, some nurture, and some a person's will.

For example, a writer has need of a variety of intense emotional experiences to fuel the fire to forge in the smithy of his soul a glowing work of literature. These experiences may be the result of happenstance; they may be recognized as essential fuel and wilfully sought out; or they may be the result of an inherited neurological disorder such as manic-depressive illness. No matter: these experiences are essential—where they are obtained is almost irrelevant.

Or consider a scientist such as Darwin. Where did he get his determination to embark on a long ocean journey when he was so prone to seasickness? From whence came his exceptional ability to find relationships where others only saw inexplicable diversity? Was it his upbringing or his genes? And would he ever have formulated his theory had not Fate offered up the opportunity to sail with The Beagle? Or consider Galileo and the suffering his independence of thought caused him. These scientists weren't mad by current conventional standards, but I'm sure many of their contemporaries thought them so.

If sometimes madness is the price paid for creativity, the creator may or may not have signed the bill of sale. No matter, a deal is a deal.