If no one is ever even slightly skeptical of your sanity, you might as well be a tree stump. See Janet Foner’s “Top ten warning signs of normality“.
When genius drops by for a visit, it often brings a demi of madness to share with the host. Problem is — madness rarely returns the favor. It just staggers in empty-handed looking for a place to crash or claiming “You owe me money!”.
Philip K. Dick is perhaps an interesting counterexample. On the other hand he was a big amphetamine user, so who knows if we was “naturally” crazy. (Probably yes, and self-medicating.) Another odd genius who loved amphetamines was Paul Erdös. Of course, many non-geniuses like Adolf Hitler loved them, too. (Hitler himself was apparently fully deluded that he was a genius.)
The first time I heard Frank Sinatra singing Nelson Riddle’s arrangement of Cole Porter’s I’ve Got You Under My Skin it occurred to me that human society is a machine to produce art (and science). The farming and wars and painful fight for survival would be pointless without them.
Another lesson from that recording occurred as I listened to it repeatedly and carefully. Over time I noticed multiple flaws, and it became clear why every masterpiece must have a flaw — because to create a true masterpiece you’ve got to let yourself go.
According to Francine Prose
One difference between art and magic is that magic can be explained. Were he willing, Houdini could have told his fans how he escaped from the chains and straitjacket, suspended under water. But the artist can never fully account for the alchemical process that turns anatomical knowledge and fresco technique into the Sistine Chapel. To create anything is to undergo the humbling and strange experience – like a mystical visitation or spirit possession – of making something and not knowing where it comes from.
According to Michael Leyton, discussing Demoiselles d’Avignon in Symmetry, Causality, Mind (p. 519),
The revolutionary action of the painting, while being central to its meaning for the viewer, as well its meaning for modern art, was an intensely personal experience for Picasso himself. During this period, Picasso seems to have turned inward and become particularly concerned with his own creativity. That is, not only was he engrossed in the products of his creativity, but he was also deeply pre-occupied with, and mystified by, the creativity itself.