There are, broadly, two kinds of writers: plotters and pantsers. Sometimes they’re called architects and gardeners, and there are other terms, too, but most everyone will recognize “plotter” and “pantser.”
Plotters create outlines. Pantsers “write by the seat of their pants.” There are many highly-regarded, NYT best-selling authors in each category. By the time their books are available to the public, no one can tell if they plot or make it up as they go along. For example, Lee Child, the person who writes the Jack Reacher thrillers, is a pantser. Many mystery novelists are pantsers. Patricia Briggs, who writes the Mercy Thompson urban fantasy series, is a pantser. Ada Palmer, on the other hand, develops huge, multi-colored, gridded outlines for her novels; she knows exactly what is going to happen at any point in her book before she writes it.
Both are good. Both work just fine. One is not better or more efficient than the other, and no one should be snide about either form of writing. You need to determine what works best for you. Also, no one is “purely” a pantser or “purely” a plotter.
I am a pantser, so I will come at this article from that perspective. When I try to make a detailed, hierarchical outline of beats and scenes, two things happen: 1) I lose interest in my story because I already know exactly what’s going to happen, so there’s no mystery or excitement any more. 2) If I try to follow my outline, invariably I veer away from the outline and go in a different direction. I have outlined plenty of successful academic papers, but I can’t outline fiction to save my life.
Like many pantsers, I do do some form of outlining. First, before I write anything, I figure out how I want the book to end. I have my climax and closing scenes in mind. They’re not detailed; in my last WIP it was “big combat in an abandoned prison, with X, Y, and Z characters experiencing A, B, and C events, followed by a resolution that mirrors the opening scene.” I also understand story structure, so I write out what will happen at each major plot or pinch point, using 1-2 sentences for each. That means I typically have about half a page of writing in which I know, basically, how the story will go. I then come up with 1-3 sentences for each chunk of 10,000 words, and I’m good to go. That is not the kind of outlining that a plotter will do! But it’s enough to keep me on track and excited to find out what happens next, and it’s flexible enough for me to adjust if something happens on the way.
Pantsers might write their alpha draft in a few months and then spend more time writing future drafts to clarify their stories. My first novel’s alpha draft was written in six weeks. My second took two years–I made six false starts. It happens.
The average 80,000 book has around 64 scenes in it, so an outliner may create an index card or page or what-have-you for each of those scenes and then painstakingly fill in the plot and character developments for each scene. They may include necessary dialogue. They might even tape each card to a handy wall and rearrange them or rewrite them until they’re happy. (Hallways and stairwells work well for this sort of thing.) There are programs like Scrivener that have virtual index cards that can help do this if you have no wall space. Or they may make the traditional outlines that we all remember from English classes at public schools. They often spend up to a year working on the outline, and then they write the book in a month or two. They might write fewer drafts than pantsers; I don’t know. (I don’t actually know very many plotters.) But even plotters still have time for discovery; they haven’t written every bit of the story in their outline, or their outline would be their alpha draft and they would be pantsers. There’s always room, even in tight outline, to discover that your main character doesn’t like spinach.