I was an English lit major in undergrad, but always have had a tiny artistic streak in me (well, let's just say I've found out I'm better at appreciating the aesthetic than actually creating it), so I took a design class.
I actually did fairly well in the class, having not much background in art to begin with. But there was one assignment I failed miserably at. Whereas all the other projects were constructive (ie, putting items together to create a finished product), this one was destructive.
We were all given a cube of plaster, about 4x4 inches. We were supposed to cut away and whittle down this cube into a 3-dimensional abstract piece, demonstrating our knowledge of lines and planes.
I briefly tried to sketch in pencil on each of the faces, trying to envision what the final, 3D piece would look like. Unable to do so and frustrated, I just started hacking away. Does anyone want to guess how that approach worked out?
The problem with working in a deconstructive art form is that there are no take-backs. Once you cut something away, the piece is changed forever in that respect. It's not like clay, where you can stick it back on, add a little bit here, a little bit there, to build something up. If you make a mistake, you may have to rethink your entire strategy, change the overall end goal entirely.
I think there are both constructive and deconstructive aspects of writing. That first draft is like the clay. You start throwing words at the page, they're coming to you so fast you can't type/write fast enough to keep up. Ideas come to you when you're falling asleep, when you're in the shower, when you're in the middle of a conversation. They just start piling up in this massive lump of raw material.
That's the easy part.
The second part has to be a little more thought out. You can't just dive in there and start hacking away. You have to have a better idea of the goals of the characters, a clear direction for the storyline. And you have to ask yourself when you're weighing each scene, each paragraph, if it contributes. If it has a meaningful place in what you envision to be the final piece. And somewhere in the process, you'll inevitably stumble upon a new idea, so fantastic you can't leave it out--yet it completely changes a main story arc. And then you have to rethink your finished piece entirely.
Yeah, that's the hard part.