When I write a short story, I usually sit down and write until I'm done. Then I go back, revise, edit, remove stuff, add stuff, read it out loud to myself, fix every minor thing in the dialogue, and then, when I'm happy with it, I'll send it to a beta or an editor, or both. That is my process.
When I write a novel, I can't just write until I'm done. I'll write a chapter, go back and read it, polish it, add stuff and take stuff out. Then I'll move on and write the next bit, and maybe do some research for some detail or another (and I need everything to be correct, so my research is meticulous), go back, reread, polish, add stuff, take stuff out. I fact, nearly half my word-count often comes in the editing process, because my rough draft is very stark, often just dialogue and a few tags, the bare minimum of detail and internal monologue so that I know what's going on. I add descriptions, embellish my language, fill out my characters' thoughts and actions, on the first rewrite.
When you do NaNoWriMo, you're not supposed to do that. You're just supposed to sit down and write. I have a really hard time doing that. If I manage 2000 words in a day, it's often because I went back and reread and added stuff to previous chapters. At the moment I'm only a tiny bit behind, and I should be caught up by this evening, but I'm not really doing this the NaNoWriMo way. It'll be interesting to see if I make it in the end.