I may have to stop reading biographies of writers whose work I enjoy. I read Becoming Laura Ingalls Wilder and The Wheel of Things (a biography of L.M. Montgomery).
Both contain excerpts of letters talking about how the authors came to hate their phenomenally successful characters and the public's demand for more stories. Laura put her foot down and refused to do any Little House books detailing her life after marriage. (There's a psychological curiousity in hating a fictional character based on yourself and your life.) Montgomery gave in to lure of cash to write book after book about a character she apparently began to hate partway through revising the first book.
It's really sad for me to think of those stories coming from a place of mercenary skill rather than a genuine love of telling the tale. But whatever the motivation, there is a connected truth in both series which rings deeper than the surface prose. They became classics and phenomena because they spoke to people across time and cultures. It's an accomplishment.
Knowing that the work became an uninspired chore brings up an old fancy I've seen used many times: that great works of art hover in some kind of limbo, waiting for the right voice to call them out. In a sidebar of his comic Midnight Nation, JMS even has his characters visit that limbo. They get to see Einstein's unified field theory and the really funny book which Dostoevsky was going to write once he got over being depressed.
I compare Wilder and Montgomery's view to J.K. Rowling who also wrote a book which became a phenomenon and was pressured to expand it. Rowling says she felt a need to tell the whole story right from the beginning. Now maybe she's just playing to the press but I believe her.
I can't think of anything more sad than having a work of heart become a resented obligation. I've worried about that, having my writing change from something I love to something I hate. I know people who would be quite gifted writers who don't want to pursue formal publishing because they're worried it would steal away the love.
It would be cool if I had an answer but the truth is, I don't know. I may never get a chance to discover if success will destroy my enjoyment. But I'm willing to take the risk.