That's a good question. Well, I never have a detailed outline, or even a Triple-O. But I do know what the main character wants and usually what the general outcome will be. If I know that, I can sit down and write and the sub-conscious will take over and create the obstacles and bleak moment that shape the story.
If toward the end of the story, I find I need a "telling detail" to foreshadow something that happens later, I just go back and put that in.
Other, and usually more productive, people have to know all the details before they start. THEY never end up with drawers full of half-finished projects where they lost the thread, either, but we all do it however we can. One way or the other, it's born in us. It may be a "right-brain" thing.
I'm reminded of that old question from Psych 101, where the professor said, "A kid is lost in the woods. I can give you beaters to comb the brush, or a helicoptor to try to spot him from the air, which would you choose?"
About 90 percent of the class chose the beaters. Those of us who took the arial view were told we were "right brain" creative people, but lacked logic, because the woods might be too dense to see our kid from the air, while the beaters would search every inch.
The "beaters" were told they were "left brain" people who had little imagination. They looked at life logically and took things one step at a time, but they lacked the ability to see the whole or the end result, rather than just the first immediate next step.
I don't believe those who are "left-brain" lack in creativity or imagination. I know some wonderful writers who are able to outline in detail and who write two to five books a year. I also know how hard I've tried to do that and how flat my efforts have fallen.
The important part of this tip is -- there's no wrong way to do it. Write using whatever method works best for your individual talent. Don't force yourself into a mold created by someone else's expectations of how it "should be" done.