Zal Batmanglij, director of the new Sound of my Voice (among others), has a beautiful metaphor for the creative process as it applies to filmmaking.
I think that filmmaking is like digging more than anything else, and it starts with Brit and I. We start digging, we see the shape of something, the outline, the top of something, and that keeps us going. Then the cinematographer comes and he picks up a shovel, and the production designer and the costume designer and then the actors come. In both SOUND OF MY VOICE and THE EAST, we’ve been extremely lucky, so Patricia Clarkson comes and she picks up a shovel. Ellen Page comes and she picks up a shovel, and then Skarsgard comes and picks up two shovels, and by the end of it we are all sweaty and tired, and we’ve uncovered something and we spend most of our energy doing he digging, so you don’t really have time to worry about budgets and constraints and “I wish I had that. I wish I had this.”
This is completely consistent with my own observations: the creative process is more akin to archaeology than architecture. It's less a matter of building something than unearthing something, one jagged piece at a time.