I am not famous, nor do I ever really hope to be, but about 10 years ago I completely lost all willpower to finish A Tale of Light and Shadow. For me it was the opposite of what GRRM is experiencing. He has become too famous to finish his story, whereas my publisher and I decided to part ways because sales were not what we had hoped due to a combination of poor marketing and perhaps the book just wasn't that good or didn't really fall into a genre that sold well.
I struggled to keep writing as other things in life drew away my attention. But I got email after email about finishing the series. I wrote other stuff but didn't want to finish the series because it felt like I'd failed and it crushed me. Anyway, eventually I just had to kick myself in the butt and start writing it again. Now I'm almost done with the final book, but writing it is still incredibly difficult, and because of it I've decided I'm not publishing anything else until I've written every book in the series.