Prospective grad students sometimes struggle with choosing the right project for their PhD, primarily because they have too many interests and could imagine doing in-debth research on any number of those. So the question is which of these many possibilities is the right project for the PhD? And the answer, in my opinion, is that it does not matter that much which one you choose, but you need to choose one and commit to it. It is this commitment that will elevate your project beyond other interests and enable it to grow into something more substantial.