"I always wondered about authors who told me that their characters took on a life of their own. I used to think they sounded a bit pretentious, but then I found out it’s true."
"Writers often report vivid experiences of hearing characters talking to them, talking back to them, and exhibiting independence and autonomy."
...the results of a survey of professional writers run in collaboration with the Edinburgh International Book Festival. Participants provided detailed descriptions of their experiences of their characters...
https://www.sciencedirect.com/science/article/pii/S1053810019304155