See, my writing process follows a very specific process that works for me, but may not work for everyone else. First, I come up with my story concept, which usually happens spontaneously and while I am planning or writing something else. Then, when I decide that it is time to write said story, I start with a somewhat detailed outline. After finishing the outline I write the story, following along the outline as best I can, taking a few minor detours along the way (the point of this post). After the first draft is finished, I put the manuscript away for a few weeks (or in the case of Wrath of the Fallen, a few months) before I come back to it. I do a complete read-through, marking up the draft with a red pen before I dive back in and write the second draft. This is always completely from the ground up, with the printed and marked up copy of the first draft on my desk in front of me. When I'm writing the second draft I change some of my wording, add more detailed descriptions, fix clunky dialogue, etc. After that I do a final edit, and send the manuscript to my editor and beta readers. After that it's ready for you!
Some authors don't outline, they prefer for the story to grow organically. George RR Martin is famous for this gardener (vs. architect) style. Others are strict about outlining. Terry Brooks used to be a big outliner, but recently he has moved away from that to give himself more of a challenge (I can't remember where I saw him say this...). Some authors don't do a second draft either. Mark Lawrence writes a first draft and then makes a few edits and he has a best seller on his desk. I am not that fortunate.
This brings me back around to my experience today. My outlines are somewhat detailed, but not to the minute detail. Mostly, I write a single paragraph per chapter, giving me a roadmap to follow, but I don't plan chapters in advance down to ever story beat. This gives me the freedom to have individual chapters grow organically, while still keeping the story on track. However, this means that sometimes the story takes its own path, and the outline has to change. When this happens, I go back and add the changes in red, preserving the original outline so that I can refer back to it. From time to time the changes in one chapter mean that a later chapter needs even more changes, because now events that may have played out later happened earlier, or an entire plot point has evolved.
The chapter that I did write today had an ending that felt completely organic based on the characters and the situation. This was not what was in the outline. Originally, the chapter would have ended on a relatively boring note, because we are building toward the climax, but not quite there yet. As I was writing though, several opposing forces felt like they would finally come to a head, and as a result one of the characters would get imprisoned. Then, I realized that the other major character in the scene wouldn't allow such a thing, and a battle ensued. It was great. So I needed to stray from the outline and the story was better for it.
Then I tried to start the next chapter, and I realized that this chapter was from a weaker POV and spoiled a twist that is going to happen in a few chapters. I tried and tried to figure out a way to still use this character to create another chapter here, to give them something "on camera" to do, but I decided that nothing felt natural here. Everything that this character could do in this situation would either be redundant to something that came before, or it would be redundant or spoil what would come later. So, I ignored the outline and cut the whole thing, moving right on to the next one (now affectionately called Chapter 19). Not only will this save readers from slogging through a redundant chapter, but it saves the narrative from slowing down just before the climax.
Thankfully, I realized that this chapter wouldn't work before I spent the time writing it, only to cut it during the editing process. This is why I outline. So that I can make the story the best that it can be before I even put pen to paper.