We could probably list many things that might be a factor. There isn't any general pattern. This goes for improvement too. Lots of people experience lots of things and some of it might appear consistent and some of it might not. It keeps switching around on us, yeah? Basically, we don't know exactly how stutter works yet, and we don't know exactly what might specifically do something. All we know is that we're going to have to keep working, each of us, to figure out what might help us in the long run. Speech therapy is known to be able to help a lot of us. That's about as close as you get to a stable component in all of this.