BTALD: What's Your Purpose?

I actually don't know what your purpose is, or mine for that matter, but I do know there are gobs of books on the subject - a whole wing of your local bookstore actually. What would be interesting would be a book about how people come to wonder what their purpose is in the first place. How does that question come up? Is it some near-death experience or epiphany or just plain boredom? Maybe after too many hours idling in front of a shiny screen the human brain is programmed to start looking inward. Like, "Why am I here?" takes on a deeper and deeper meaning, from "Why am I still on this couch" to "Why am I not out saving the world today?" Or, not. But something is setting us off, or there wouldn't be so dang many pastel-colored, inspirationally-titled books about finding your purpose out there.