I find that I have more stress from concern about whether the writing really is moving forward even when I'm putting words on the page - i.e. will the words I'm writing 'work' - than from writers block. Always at the back of my mind is will these words make the work less cohesive - am I moving backwards?

But in general we manage what we measure and we normally have a word count but no easy way to measure whether a work is really coming together.