In working on your WIP, what is the hardest thing for you?

Characters?
Plot?
Setting?
Getting started?
The ending?
Slogging through the middle?

For me, it's slogging through the middle. I usually know how it starts and how I want it to end, but getting there is -- often -- torturous. It's always riddled with questions, second-guessing, mental kicking myself, and severe self-doubt.