George R R Martin talks about two archetypes for writers: Gardeners and Architects. The architect will plan and plot their story, knowing what happens to who from beginning to end before ever writing a single word. The gardener however will go in blind, knowing only the barest of details and discover the story as the write.
In truth, most writers sit somewhere between these two polar opposites. But the approaches are so vastly different that people usually identify with one extreme or the other.
I’ve always thought myself a gardener, although one that does a lot of thinking. I will have a good idea of the milestones of the story and the overall arcs of both character and story, but anything inbetween is up for grabs.