Some only need to plan the big picture before they dive in and then free-wheel it throughout the duration of the project.
Others need to plan the big picture as well as the nooks and crannies in between. The start date and the release date. The working hours. The blocks of time within each day and the elements being worked on within those blocks.
Yeah, you can wing it only when motivation strikes. Lots of people do that. Lots of people never actually see their goals spring to life either.
Or you can plan it one way or another. Big or small. Motivated or mundane, and build the project one decision, one hour, one element at a time.
Anyone can wait for motivation. But those who create just go build it.