The hardest thing I ever wrote was probably the classroom scene in my sci-fi dystopian WIP.
I'd created the world for the story long before I really started writing it, and I needed this classroom scene to provide the history behind how all of the characters got into the place they were in the story. And I mean, I'd been dreaming about this scene for months. Constantly making notes about it, adding details for when I'd finally get to it. The world and its history were fully formed in my head, and I was just so excited to get it down on paper.
But then I got to that point in the story, and I just....choked. I struggled for *so long* on it. I finally got it all out, and it's mostly an infodump that I'll probably have to majorly revise, if not slash completely. That is, if I ever get back to that story... I started it five years ago and it's maybe halfway done. At least I've got another project that flows a bit better!