I think understanding what you want to share helps solve the major stumbling block that leads to thousands of blogs with one entry that is effectively hello-world. If told to draw anything, most people will sit with a blank page. However, if they are told to draw a castle, those bounds give them the freedom to start and create, and it can evolve from there.
What are you into to? What hobbies do you have? What do you know, or have opinions about, that others might be interested in? This is your theme, the “real thing”. Writing, podcasting, or video production, without this usually falls flat after 1 or 2 attempts, and it makes it impossible for a habit to form.
If you’re already into something and doing it on a regular basis, then you’re just writing about, talking about it, or recording what you’re already doing or thinking about all the time anyway. The content and ideas can flow more easily, especially at the beginning. Not to mention, being more motivated to make the content, since it’s already a passion.
So many people are trying to make content about nothing, because they aren’t really doing anything else… and this is where friction is born. Do something you find interesting, then share that thing and your perspective on it. Start with the doing, not the sharing (writing, podcasting, and YouTubing is the sharing).
Hopefully this clarifies what I was getting at and resolves the chicken/egg thoughts.