The following quote from Irving Stone describes how Michelangelo worked on his Pietà.
He carved in a fury from first light to dark, then threw himself across his bed, without supper and fully clothed, like a dead man. He awoke around midnight, refreshed, his mind seething with sculptural ideas, craving to get at the marble.
I really enjoyed reading The Agony and the Ecstasy. I have no idea how accurate the depiction of his life was, but I felt like it let you enter the mind of an obsessed genius. And it is probably redundant to say “obsessed genius.”