I think I fear success more than I fear failure. Failure?... bah, I'm used to it.
Success on the other hand would be hard to get used to. Imagine how hard it would be, to earn 250K a day like J K Rolling??? I would be permanently scared of mismanaging all that money, having to rely on experts to do it for me, loosing my independence, sleepless nights, being taken advange of by my finance managers and staff, distrusting everybody, and... being ambushed on the street on my way to the shops to buy ice-cream. I probably would have to buy a big mansion, with a high perimeter fence, video cameras and muscular security guys patrolling around the clock. SAD... If I succeed in writing a good enough book, I think I'll probably give the publishing rights away to chariy so I won't have to deal with all that. Ever...
There are worse things than fear of failure. Fear of dying, or maybe not so much the fear of dying, but the fear of what might be killing you slowly. I've been there. It's real. Failure is not real. It's just a state of mind.
Happy writing! (You are supposed to enjoy it. Don't torture yourself.)