“You can always edit a bad page. You can’t edit a blank page.”
-Jodi Picoult

A lot of writers and artists struggle with starting. One reason a lot of people struggle to start is that they fear the blank page. It’s empty, it’s new, and any mark you make must be perfect.
Wrong! It may be ridiculous, but one way to conquer your fear of “messing up” the blank page is to purposely make a mess of it before you seriously begin. Doodle something silly in the corner! Scribble the whole page and start seriously on the second page! Write something silly that doesn’t make sense!
Sometimes the hardest part is starting.
And if this is something you’re struggling with in the middle, not just at the beginning, that’s also okay. Take a break and do something ridiculous. Get through the fear. Or even just continue and accept that maybe your first draft (or second, or third) may not be perfect and that it doesn’t have to be.
Edits can always be made later. But you can’t edit what you never wrote down.