It's already a few years ago, that Merlin Mann and John Gruber talked about the concept "Obsession x Voice".
The thing is that you have to know what you're obsessed with. That's hard. You could be really sad to not know what your obsession is. Not knowing is not the biggest problem however. Deep down I know I have an obsession that I would write about. I have written about it. Quite a lot, actually.
And some time I have written a text file with 87 lines of things that interest me. And while I review that list now, I see that it's incomplete and other things are less important to me than they were the day I wrote that list.
But could I say that even one of the things on that big list is an obsession? What am I obsessed with? What's the one sentence that describes what I do and want to do more than anything else?