What energy guides you to a particular subject? Do you find yourself asking, “I’m interested, but will others be?” Does this matter to you in the original subject gathering process?
I think I know a promising subject — for me (not necessarily for anyone else) — when I see it. The problem is, a lot of not-so-promising subjects can also look promising at first, so I’ve learned to let all potential subjects sit for a while — long enough, at least, for my initial rush of enthusiasm to wear off.
When it does, I can assess more clearly — a week, month, or year later — whether a subject still intrigues me and has the potential to do so for however long it would take to research and write a book. The best sign that a subject has that potential is when I find myself thinking about it while I’m working on another project that I’m perfectly happy with.
“Will others be interested?” is the trickiest of these questions. I’ve been wrong before, and even when I’ve been right, it’s taken a lot longer for that to become clear than I would have thought. But really, it’s my job to tell the story in a way that others will be interested in, and if I don’t see a way I can do that, I need to either research a little more until I figure out that way or else look for another subject for whom I can better convey my enthusiasm.