Here is Louise Glück telling Poets & Writers about her process:

When I’m trying to put a poem or a book together, I feel like a tracker in the forest following a scent, tracking only step to step. It’s not as though I have plot elements grafted onto the walls elaborating themselves. Of course, I have no idea what I’m tracking, only the conviction that I’ll know it when I see it.

One might imagine it’s actually better for the writer when they have no idea what they will find.