Artists, Could you describe you visualization process?

Specifically I am wondering how you visualize your works prior to doing any physical work. I’m thinking about 2d works like painting and drawing even digital works, but probably applies to 3d works like sculpture, etc.

When working on a new piece do you fully see what you want your final image to be or do you see a basic structure that will evolve as you physically work on it. What percentage of the final work do you visualize prior to starting work.

I really open this question to anyone, whether you are a closet artist or a galleried professional. There is no right or wrong answer. Sorry for the vagaries, run with it.