I will agree that a lot of things I do are unplanned. Pretty much each book I start happened when I sat down to write something, anything. I even add in characters or plot points on the fly.
But I tend to plan out after a while. I guess it's what helps me stay focused. Although, I don't always use what I write out. I'm flexible. If it doesn't fit when I get there, I toss it and come up with something new.
Like my newest series, which I'm hoping can be published with Tapas soon (not currently available on my profile, basically), is also like that. I plan out my chapters, like the main feel or important scenes I want, but it may or may not change when I sit down to look at that part of the story.