I suspect a lot of people aren’t sure what’s the top idea in their mind at any given time. I’m often mistaken about it. I tend to think it’s the idea I’d want to be the top one, rather than the one that is. But it’s easy to figure this out: just take a shower. What topic do your thoughts keep returning to? If it’s not what you want to be thinking about, you may want to change something.

Paul Graham, “The Top Idea in Your Mind”