the why in writing
Talking or writing about the things you're interested in is a good way to generate new ideas. When you try to put ideas into words, a missing idea creates a sort of vacuum that draws it out of you. Indeed, there's a kind of thinking that can only be done by writing.
How to Do Great Work

Writing increases your rate of revelation. This is true irrespective of the subject because writing is a process of reflection, assertion, and iteration.
Writing clarifies your own ideas. Writing begets new ideas too. Writing lets you explore ideas in depth even if you won’t have time to act on them all. Writing shows people how you think and lets ... See more
Writing clarifies your own ideas. Writing begets new ideas too. Writing lets you explore ideas in depth even if you won’t have time to act on them all. Writing shows people how you think and lets ... See more
Anu • Writer-Builders

All novels, short stories, and plays, and most poems, are about human transformation. The subject of the novel is the human spirit and psyche—how the characters interact in their relationships with other souls and with the world in general.
Walter Mosley • This Year You Write Your Novel
The best writing prompt for when I'm stuck is simply "be more honest".
Metamorphic words…attempt to change the author in unpredictable ways, which you can think of as an intrinsic reward of sorts…If you don’t like, or are bored with, who you are right now, whether as a writer, or more generally as a person, you can write yourself into an unpredictable new version. It’s a kind of disruptive self-authorship lottery.
Writing is a great way to excavate an emotional reaction and find the why behind it.