I had a few ideas for this topic from Long and Short Reviews, and came up with one that I am frequently faced with as a writer - writing a synopsis.
A lot of writers will tell you they hate this part of the process. Condensing your work down to a page of text, trying to establish what best to include to emphasise the right plot points and depict your characters properly. If you get it wrong it can affect whether or not your story is accepted - I had to redo my synopsis of The Hand He Dealt after a publisher I'd submitted to rejected it on the grounds that it didn't sound like a love story, which obviously meant I'd screwed up somewhere.
I've found it slightly easier with shorter stories but even then it's frequently a nightmare. My last short Spiritwalker had so many plotlines I thought I would never get it onto one page.
And, as I've nearly finished my new short Hyperventilating, I'll have this to do again before long. It's an unavoidable part of submission, unfortunately.
So what task do you wish you never had to do again?