I'm starting to learn the hard way that a first draft does not have to be perfect. Somewhere along the line I started to be extremely hard on myself about every single line I wrote, to the point where I began to question, does this make sense? does this fit? does this sound natural? Delete, delete, delete. That's why I avoided NaNoWriMo, because I knew I wouldn't be able to produce that many words in such a fast amount of time without going insane. Bottom line: I don't trust myself as a writer.
So, I've written over 10,000 words on this new draft and it has taught me to write and think later. So what if parts of the dialogue doesn't make sense yet? That's what editing is for. And as we all know, we are going to be editing our manuscripts not once, not twice, but many, many times. That's when we fine tune those lines and create layers in the story.
Trust yourself as a writer. Sit down and produce. Edit later. Have fun.