[From "The Art of Art": The art of the Process > Vision and Execution]
To put it very simply indeed, every work of [deliberate] art goes through two main stages: vision and execution. In the vision stage we collect information, raise different options, and finally sum it all up with a quick sketch of the finished work as we imagine it. Only after we had decided what the finished work is going to be like, we start executing the work itself. We could say that every [deliberate] creative work actually gets done twice: once when we form and sketch our vision, and again when we realize it.
The important thing about working with a vision is that it provides a clear framework for our efforts: we work until the result is close enough to our vision, and then we can stop. This frame of mind is fundamentally different from the open-ended "walk in the park" approach of casual art, in which we have no idea where we we're going and we only stop working when we're fed up or have ran out of time.

Deliberate work gets done twice: once when we form and sketch our vision, and again when we realize it.

Deliberate writing: sketch and execution.
Films are also made twice. Animatic vs. the finished result.

Sculpting is also done twice. Quick sketch vs. final work.
Computer games, AKA game level or maps, are also made twice: first the fully playable vision sketch, then the final level.