I’m not an expert, but for me, yes, there has been some building up to it. Establishing the habit of daily writing and putting no pressure on yourself for that writing to be good gives your mind permission to tell all the stories.
I have this voice inside that tells me that my stories are unimportant because other people have had it so much worse, and it takes a writing habit to quiet that voice down.
I think there are a lot of reasons writing heals, but the one I mentioned about making implicit memories explicit is so huge. And I guess that would probably be one of the aims with exposure therapy, but I agree this approach is softer.
You are in control when you write and can try different approaches, such as writing a fiction where things went differently than they did in reality. Or you can write about something traumatic but write about it as if you’ve healed from it, even if you haven’t yet, and just writing that might help you heal. Or you can just be brutally honest about how much you hurt and aren’t healed. I’ve never forced myself to write about anything or to choose any of these approaches beforehand; I’ve just developed the habit and then let myself write without overthinking it, and so it gives a voice to buried feelings sometimes.
You also can then choose (or not) to share your writing, which can be an added therapeutic step, to be able to take this pain that you’ve had to bear alone and show it to someone who can understand and care.