Besides being a painter, I'm a writer. Writing comes easiest to me when I have a clear vision of where the writing will go. Though the analogy is an old and tired one, it's fitting; a successful trip requires a good map and a definite destination. When I write a magazine article, such as a feature interview or a technical column, I know my destination and how I'll get there. The articles follow an established format.
On the other hand, I have the hardest time with fiction. Whereas writing non-fiction is like a drive down the road to a place I've been many times before, writing fiction is more like a backpacking adventure into the wilderness. Although I always have a trail map, I'm often sidetracked. Sometimes a secondary trail looks more interesting. Sometimes I get confused when the trail forks. Sometimes I wonder if the hill to my right might give a good view. Sometimes—well, you get the picture. The plot outline I so meticulously crafted gets tossed into the trash, or at least heavily revised, when a character does something unexpected.
But perhaps not surprisingly, taking a turn that's not on the route, or letting the character do something outside the outline, can lead to a richer end.
Need I say it's the same with painting? Having a clear vision of where you are going will take you to a satisfactory outcome soonest. But sometimes, not having that clear vision, despite the detours, obstacles and time lost, will take you to a place that is far better.