Heya Maze,
I will try! I'm not a good explainer in general, though.
I found
this article from HP Lovecraft early on with some tips on how he approaches writing, and he has this section on early ideas:
"
...usually I start with a mood or idea or image which I wish to express, and revolve it in my mind until I can think of a good way of embodying it in some chain of dramatic occurrences capable of being recorded in concrete terms. I tend to run through a mental list of the basic conditions or situations best adapted to such a mood or idea or image, and then begin to speculate on logical and naturally motivated explanations of the given mood or idea or image in terms of the basic condition or situation chosen."
He's rather long-winded but it really resonated with me (and rather like parenting advice, I think it's generally a good idea to go with writing advice that "resonates" with you.)
So with Anchor, I started with the core conflict: two women who share one life, and one of the women is suicidal, which will end both their lives. MC1 starts confident -> becomes conflicted -> ends despairing. MC2 starts suicidal -> becomes conflicted -> ends resilient. The actual events didn't really matter to me. I don't care, at this stage in the process, what causes one to be despairing, or one to be conflicted; any of that I'm happy to change. The main thing is that those emotional state occur.
For MC2 in particular, I had her ending scene written well in advance of most of the book. That feeling you get, when you've been put through an emotional wringer and you're a quivering pile of metaphorical jelly but still standing--JUST--is what I was going for, so that's what I wrote her end-scene to depict. I had a couple of other core emotional scenes (the first antagonistic clash between MC1 and MC2, things like that) but actual plot points or events, I constantly changed, rewrote, or rearranged as needed to serve the ending scene and to create the end emotional states that I wanted.
I'm doing some revisions now and while writing them out, I worked out a better way I could do the plot that would be stronger and more logical. It would require scrapping some of the emotional "pillars" though so I think the story would be less impactful; I've gone, in this case, for a weaker plot in exchange for what is hopefully a stronger emotional arc. (And this is where plot-driven novels would diverge from character driven, I suspect.)
Sorry to use my own stuff but I find it easier to explain with a practical example.