Writing is Rewriting?

If writing is rewriting, as most writers will say it is, then is constantly revising the same script over and over again actually writing?

Okay, so I'm not constantly revising it over and over. It's just that, with screenwriting, there is so much tweaking and rewriting (over a comparitively small number words (compared to novels, for example)). This one script, one of my best, is the one that my friend/would-be manager is going to take out to the industry. And I'm trying to tighten it and make it better. And it IS better.

But I can't remember the last time I started a new script --from scratch-- and completed it. This may just be my own paranoia and neuroses. I don't know. I'm just concerned that I am not growing as a writer if I am still trying to make this one script good (or revisiting other old scripts, for that matter).

I'm a writer, so I"m naturally going to question my own abilities. So I don't know, maybe I should just strart writing and stop thinking about writing.