Why Can't I Decide?

I've known for two and a half years now that I was going to have to write a dissertation someday.  In all the classes that I have taken I have read research on many topics and would wonder "Could I write a dissertation on that topic?"  I can't even count the number of ideas that I have had over the years - adolescent motivation to read, reading recovery, how policies affects classroom teaching, how policies constrain teachers, complex adaptive systems and classrooms, writing workshop, professional development - the list goes on and on.  My interests have varied depending on the reading I was doing for class and how that reading connected with my experiences as a teacher and a learner. 

Since I've also been working as a Graduate Research Assistant for most of that time, I have been mentored in many aspects of research and writing, as well as things like working on a grant, organizing a regional conference, faciliting research with outside evaluators, etc.  Every time I learn something new, I think "How could I turn that into a dissertation topic?"

Every time I go to a conference I sit in sessions about various topics and think to myself "How could I do research on that topic?"  Could I do a dissertation that was more practitioner oriented?  Could I do a theoretical dissertation on complexity and literacy?  Could I do a review of research dissertation on writing workshop?  Could I do a case study of a writing classroom?  Could I do a dissertation on a professional development model?  Could I do a dissertation on policies and their unintended consequences?  Could I do a historical dissertation on the work of Marie Clay?  Could I do an ethnography of a classroom looking for reading writing connections?

I've read books on how to write research proposals, how to do qualitative research, how to do quantitative research, how to write a literature review, how to write an education dissertation, etc. I've had conversations with other doctoral students about dissertation topics.  I've met with professors about potential dissertation topics.  I've gathered and read research on many different topics just to see if I was interested enough to consider it as a dissertation topic.  I've written a literature review on professional development and a research proposal on a case study of a classroom using writing workshop.  I've gathered data on informational text and read about that topic as a potential dissertation topic.

I've been all over the place . . .

Why can't I decide?