When other writers talk about characters "getting away from them" or "out of their control", I have to confess, I'm at a bit of a loss to understand that. I'm not saying that in a "I'm right, they're wrong" sort of way-- it's just a difference in process.
For example, I write with a well-established outline, so my major character's goals, intentions and actions are largely worked out in the outline phase. In the drafting phase, none of them are going to "surprise" me, nor do I have a conflict between What The Plot Needs and What The Character Needs, because I've already taken that into account. If one is more of a pantser, I can see how the process of pantsing a first draft can create these Plot vs. Character conflicts, where what a character needs to do is at odds with what you, the writer, need them to do for the plot.
However, notice I say "major characters". This is a crucial distinction, because it's the minor characters where those surprises and discoveries can come into play, mostly because they aren't even taken into account when the outline is written.
Take, for an example from Thorn of Dentonhill, the character of Hetzer. Hetzer initially existed solely because Colin needed someone to talk to in a scene. I establish that Colin is a street captain in the Rose Street Princes, so I need someone for Colin to be a captain of. Hetzer was never in the outline. Nor were Jutie or Tooser, the other Princes in Colin's crew. So, when I reached the point in the story where Colin makes a crucial decision and acts upon it... Hetzer is by his side. Hetzer got elevated to being a crucial part of the story-- even being the POV character for a couple scenes-- because it made perfect sense in the moment. He stepped up in the story because that was exactly what Hetzer would do.
Now, I'm not going to act like this was some sort of out-of-my-hands divined-from-above thing. This was a realization I made when writing the scene, and that realization made it clear how the details of the rest of the story played out. I could have ignored that realization, made a different choice. I know my first choices aren't always the best.* Heck, a major thing that became a crucial character element for Minox in A Murder of Mages wasn't even in the rough draft.
My point is this: you know who your characters are. You know what they need and want, and what choices they'll make because of that. How that manifests in your skull during the process.... that's not for me to say.
What IS for me to say is that I'll be signing at the Penguin booth at New York ComicCon at 4pm on Sunday. That is LITERALLY the final hour of the con, so if you're there and you still have strength to shuffle on over to the booth, come say hi. ALSO, as I said before, there's a multi-author Post-NYCC Event in the Penguin Random House offices on Monday at 11am, and if you can come, you totally should, because they're giving away free books, and there are many authors there who are much cooler than me.
*- Back in my theatre days, my usual costume/set/art director had a mantra: "Your first three ideas are wrong." A bit pessimistic, but it highlights a key point of it being okay to work through bad ideas to get to the good ones.