focus if you want $$$$

I have been told that in order to make money blogging your blog must be focused. But I have many and varied interests everything from documentary filmmaking to traveling to reading Jane Austen to the following politics so how can I focus my blog only on one thing. Well I'm going to have to if I want a blog that makes money. since this blog is just starting out this will be my equivalent of the junk drawer blog. I'll throw all my wanton and scattered ideas here, only to sort them out for actual moneymaking websites later.