Planning a painting or any project reveals that planning is about levels of control. Sometimes a plan is so cursory that it's just a light sketch. More of a push in a certain direction than a map to get to a particular place, whether physical or metaphysical.
Because the first painters I ever saw in action were Edward and Maxine Runci, I followed their example and only created a light sketch with paint on the canvas. With experience that habit became a philosophical approach. I learned that for me my commitment to creativity was the practice of creativity in many forms.
Because painting is risk-free (in the sense that parachuting isn't) I prefer that what happens after the beginning of a painting be a bit of a serendipitous surprise. I like the dance between control and lack of control. I've learned that controlling an image with a very light touch can lead to something better than I could have consciously planned. This can get me in trouble sometimes, but that's what gesso is for. Gesso is a thick white primer that can cover months of seeking without finding. If gesso isn't enough, I move on and move the piece to the burn pile.
Whatever the outcome, the risk of failure is worth the satisfaction of creating something new.
Some artists call this approach stream of consciousness. I suppose that the word stream refers to the sense of flow I feel when this approach is really working well. My book, Paint Happy! North Light Books, 2002, 2004 presents a version of this approach, albeit with the light touch of control being the restriction of keeping the imagery upbeat.