From Virginia Woolf’s diary for Tuesday 11 May, 1920…

“It is worth mentioning, for future reference, that the creative power which bubbles so pleasantly on beginning a new book quiets down after a time, & one goes on more steadily. Doubts creep in. Then one becomes resigned. Determination not to give in, & the sense of an impending shape keep one at it more than anything. I’m a little anxious. How am I to bring off this conception? Directly one gets to work one is like a person walking, who has seen the country stretching out before. I want to write nothing in this book* that I dont [sic] enjoy writing. Yet writing is always difficult.”

Yep. As someone who is working on a book, I can vouch for this.

*She was working on ‘Jacob’s Room’.