I think I've mentioned this before: you can plan all you like, but you never know what'll unfold while writing until you're writing.
You plan things and then they change. Not everything. If that were the case, what writer would ever be able to plan anything? Things change, though. I've never labeled myself as either an architect or a gardener; a planner or a seat-of-the-pantser.
I don't believe in writer's block. I do believe that if you're a writer who starts writing, you're going to end up going somewhere just as surely as if you were driving a car. The car doesn't care whether you've planned a trip or not.
The general's plans seldom survive the battlefield.
This came up for me again while figuring out a scene and then writing the scene. It sounds simple that way, but what happened was more like acting to me. Or maybe directing. Maybe both. I found myself playing out the scene in my head, according to my notes. I was figuring out where the characters were and what action was taking place. While getting into the characters heads and letting get into their heads so I could get detailed on their movements and dialogue, one of them changed the crowd scene. In that moment, the protagonist started talking with bystanders in the crowd scene. It's something that wasn't supposed to happen and resulted in an impact that created ripples upon ripples.
Don't sweat it. I'm not talking about impending tsunamis rising off the coast. It just means extra work for me and a bit more depth for the story. These are not bad things. This is just the sort of thing that you should probably expect when you turn your brain into a forum for multiple personalities. Getting into your work, just as when readers lose themselves in stories, you allow your imagination to take an active role in its development and open yourself to the possibility of surprises. That's when you've arrived at what people describe as the characters writing themselves. It's really still you, but you're playing all the parts in the puppet show. At least you've given them something specific to talk about. It's not a disorder if you're in control of it.
For some people, it's group therapy. For others, it's a playdate with some imaginary friends. How the story is told and how much of it ends up on the pages is all for you to decide. Your writing is whatever you decide it is to you. If you can't, don't worry--there's always somebody out there who'll be happy to slap labels on you and whatever you do. When you're creating it, though, however you get yourself from start to finish, make sure it serves you-- whether exercise, entertainment or something else-- as whatever you need it to be.