The thing about writing is that the process doesn't always move at the same pace. I never understood those who sit down every day and say they are going to write 500 words or 1,000 words. Not every scene in a story can be written according to a schedule and I've always found the only way to work is to let the words come in their own time.
This is especially true with crucial scenes, ones that are meant to answer questions that the reader has formed up to that point, while at the same time setting up the next big change in the story. These critically climactic scenes require careful attention. Things need to be revealed in a certain sequence, characters have to speak in certain tones, and the story must maintain a certain rhythm.
Today, I finished one such scene. After day upon day of working on it and crafting it just the way I wanted, I finally inserted a page break and moved onto to the next chapter. It's grueling when these scenes take a long time, but so rewarding when they're done.