It is so easy in this day and age to simply consume the ideas that others have created. It's so easy to admire the work of others, and to continually consume the ideas of others.
I think this happens to a lot of writers. It's easy to get caught saying "I need to research more," using the logic of incomplete scholarship to avoid the risk of revealing one's own ideas. But that's what academic work is really about, right? It's about finding new ideas, new truth, territory not yet discovered. I was talking today with an old acquaintance and he was telling me he was doing research on the limits of quantum computers. "It's like science fiction," I said. "Just mathematics," he replied. It is just mathematics, I understand, but it is also like science fiction: it explores possibilities for things we've not yet done. It is, in that sense classic academic research: it presents a view not before revealed. Whatever the field--mathematics, philosophy, the social sciences--whatever, the purpose of academic work is to produce something new.
The source of that something, I suggest, is only to be found in our unique perspective of the world--a perspective based on what we have studied, surely, but also based on what we make of what we study--on what we take from the data we gather (a process inevitably shaped by the choices we make individually).
It may never be that the perspective that we can develop on our own develops into anything that shakes the world. I think most of us both fear and hope for this: we all fear and hope for fame and influence. We won't find it by simply consuming the ideas of others, unless we find some novel way of seeing those ideas--and thus make them our own.
Of course searching for world-shaking ideas is not something that is always associated with research. Much search for knowledge has simply been the individual driven by personal interest in understanding some issue. But again, this is a search for something new.
Even when consuming the ideas of others, an academic has to engage in an active way: not simply seeking understanding, but seeking to see how the ideas can be used, to see where they are strong and where they are weak, where they surpass other available ideas and where they are inferior, etc.
If we are writing and actively working on a writing project, then to the extent that we remain continually engaged in that project, our consumption of ideas is much more likely to lead to our finding useful material to bolster our written project and to increase our own intellectual sophistication with respect to our project.
If, however, we are engaged in consuming ideas as a prelude to writing, we will continue to simply consume. The act of consumption alone does little to bolster our own ability to actively engage with the material, and that is an ability that we have to exercise.
In short: if you want to write a dissertation (or anything else, really) start writing now. You can always do more research while you're writing, if necessary.